The adventive Crassulaceae of Rangitoto Island, Hauraki Gulf, New Zealand (en) PDF Imprimer E-mail
Crassulaceae in habitat - habitat
Écrit par Eduart Zimer   
Lundi, 29 Mars 2010 16:39

The adventive Crassulaceae of Rangitoto Island, Hauraki Gulf, New Zealand

 

Photos


The young volcanic island of Rangitoto, Hauraki Gulf, New Zealand is a unique and very dynamic environment evolving rapidly and significantly changing its biological profile in only few decades or sometimes even in a matter of years. I have already written few words about this island in my article about the Rangitoto naturalized Aeonium plants (Zimer, 2008b) so that I will largely skip this time the formal introductory paragraph about its habitats. However, one thing has to be underlined – compared to the mainland it has developed totally different vegetation patterns.


At present about 85% of the surface is covered by vegetation. In fact it is a true mosaic of vegetated patches, initially spreading from spots where few vascular plants have managed to establish, alternating with more or less larger areas of bare lava fields, but beside the local variations there are – much simplified – three main vegetation types, according to the different substrates:

 

  • The vegetation of the low basalt fields. These areas cover most of the island and are dominated by the native pohutukawa (Metrosideros excelsa), Metrosideros robusta and their hybrid swarms (fam. Myrtaceae), representing in most areas the bulk of the bush-like vegetation (1). This light bush is not very compact, nor continuous, but it supports actually a collection of sub-canopy micro-environments, sometimes with very distinctive features and local characteristics.  An example in this regard is the kidney fern (Trichomanes reniforme, fam. Hymenophyllaceae), an odd sub-succulent true fern forming dense groundcover patches with localized occurrence.  

 

  • The vegetation of the scoria cones is dominated by kanuka (Kunzea ericoides) and manuka (Leptospermum scoparium), but also other scrubs like Myrsine australis and Olearia spp. There are also two introduced species with very high occurrence, Erica lusitanica (fam. Ericaceae) and Hypericum androsaeum (fam. Hypericaceae), escapes from an intended botanical garden. The vegetation of the volcanic cones has nowadays the appearance of a light bush, is a very composite mix of several plant species. This mix also includes both Metrosideros species mentioned above but they are pretty much a casual occurrence. It appears that the vegetation has established and developed later in the cones area, possibly due to subsequent volcanic activity (few centuries of sustained ash and tephra emissions accompanied with fumes) after the lava flows have ceased, but strange enough it is the only place on the island where pockets of reasonable deep soil-like substrate have been formed in a relatively short time.  

 

  • The vegetation of the shores. The typical shore vegetation consists (depending also on the shore characteristics) of grasses like Agropyron junceiforme, or the wooden mangrove Avicennia resinifera, or the succulent halophyte  Sarcocornia quinqueflora ssp. quinqueflora in open spaces mostly on lava blocks within the splash zone, which also occurs locally forming from dense isolated mounds to large patches covering the salt marsh area. These plants don’t mix, but rather tend to become dominant locally. The cosmopolite sub-succulent Calystegia soldanella is also quite common especially in places where sand accumulations occur. As in most of the cases the bush does not come down to the waterline there is a relatively less vegetated narrow strip, an open invitation for xerophytes and halophytes alike. This is the place where all Rangitoto adventive succulent plants have managed to establish, some of them in large numbers.

 

With only few exceptions (2) all adventive succulent plants on the island belong to Crassulaceae originating from different parts of the world – South Africa, Mexico, Europe, Canary Islands or even tropical Asia. I’m not trying to read something into this – in fact all exotic succulent plants from the island are garden escapes and represent actually plant groups that used to be very popular in New Zealand gardens many decades ago. However, it appears that the Crassulaceae do particularly well here on mineral substrate, in hot conditions at ground level (the black basalt fields can get extremely hot in direct sun), with the quasi-constant deficit of water, even without a proper porous substrate capable to store moisture for some time and with a very generous natural ventilation drying up the thin layer of rocky soil (if there is one) even faster.


With no exception all Rangitoto adventive Crassulaceae originate from the gardens of the former baches, they are all cultivation relics or escapes. Some have hardly managed to survive, but some others thrive like nowhere else in the wild and have become due to their extreme invasive behaviour a real problem for the habitat. Via neglected gardens placed within in a very versatile environment several other plants have managed to spread throughout the island raising concerns about Rangitoto’s future. The exotic species had a significant impact on the vegetation development and on the vegetation patterns on Rangitoto, even severe infestations with highly invasive plants occurred in some parts of the island. This problem was acknowledged as early as 1937, but little has been done until after the World War 2 has ended.  Apart from how the Crassulaceae have been introduced here, there are generally three obvious sources of exotic plants on Rangitoto – deliberate introduction, garden escapes and natural dispersal from adjacent sites (mainly Auckland’s Devonport, Northcote and Motutapu Island), however, the later being of lesser importance.


In the early ’50s, in the height of the dispute between the bach owners and the environmental bodies, bach owners have claimed that exotic plant infestations have not started from their gardens as significant infestations were discovered in remote and almost inaccessible parts of the islands (Andrea Julian, 1992), but rather than prove their innocence this has proven that invasive plants may establish far away from the initial infestation source if adequate dispersal means are available. Strictly relating to Crassulaceae – the abundance of succulent plants around Yankee Wharf, a place rather isolated from the former baches and other dwellings, clearly states that despite of a sustained environmental control in later years, points rather to a very effective “migration” from abandoned gardens to remote areas where all conditions to establish successfully were present.


It is quite hard to produce a final account on this matter, but rather a snapshot of the existing status in certain moments. Some well established colonies – like the Aeonium colony in Islington Bay – have been almost destroyed in the past in a matter of days (Zimer, 2008b). Most sites are periodically checked by the Department of Conservation, some very thoroughly, but some are more or less neglected for longer periods of time and here can establish in time a very interesting additional flora. In most of the cases the medium term target is Zero Density Control (no adult plants on site) with the Eradication as an ultimate goal, but in the meantime Sustained Control keeps infestations within reasonable limits. It becomes quite clear that most of the adventive Crassulaceae have no future in Rangitoto.


However, although it is not the purpose of this article (but it might become in time one of my projects), I insist on the idea that preserving some exotic additions in controlled and strictly limited “enclaves” might be achievable with less financial effort than eradication and could also create iconic landmarks.  


I have done my best to present a full picture of the species that were at a time or another on the island. I have consulted therefore both botanical and environmental papers currently available, but also had an open mind and listened and looked also into unsubstantiated claims from well known connoisseurs of New Zealand flora (3). I have added to this my little knowledge gathered over the last four years I am particularly interested in Rangitoto. However, because of the continuous vegetation check some garden relics or casual occurrences could have been eradicated since recorded on the island – and it might be true for a handful or so of plants. Nevertheless my aim was to compose a complete list of the adventive Crassulaceae that have been observed in Rangitoto in time to which I have also added few doubtful names. Needless to say that I have seen less than half of the names plants here, but there are still large areas I haven’t covered during my four trips to Rangitoto.


And here we go with the list:


Various Aeonium spp. & Aeonium hybrids. Several names have been referred to Rangitoto by botanical and environmental papers, some in error, but also at least one true species has been (with a single notable exception – Wotherspoon & Wotherspoon, 2003) completely ignored. I have detailed this aspect in my 2008 article published on the ICN website. In such an uncertain environment, haunted every now and then by the controls of the Department of Conservation, it is actually very hard to support especially the old references with fresh field collections or pictures, things may have dramatically changed in time. I would like to add that I could document just 3 of the species previously mentioned: Aeonium ciliatum (Willdenow) Webb & Berthelot 1841, Aeonium haworthii Webb & Berthelot 1841 and Aeonium undulatum Webb & Berthelot 1841. Hybrid plants are actually very well represented in Rangitoto with more or less obvious parentage as hybridization seems to occur freely.  I would like to mention just two striking forms – an obvious Aeonium undulatum x haworthii (I will refer this plant as Aeonium ‘Islington Bay’) and what I think is a backcross of this plant to Aeonium haworthii (referred as Aeonium ‘Rangitoto’ – Zimer, 2009c), a very special plant worth having a name!


There is also another name mentioned for the first time in Rangitoto by P.B. Heenan & al. (2002) – Aeonium x floribundum A. Berger 1930. According to this account the plants are “locally established near high water mark” which suggests the Islington Bay colony rather than Yankee Wharf. As I don’t know this plant at all it is impossible for me to state that is was out in the field or not during my first visit to this location, while the colony was still intact.


There are two locations in Rangitoto where I have seen Aeonium plants. The first is a very compact colony at Islington Bay, just south of the wharf, with possibly thousands of plants (before being checked by the Department of Conservation in or shortly before January 2009) on a very narrow coastal rocky strip between the sea and the coastal track. It used to be rich in various species / forms and my opinion is that it is a real loss. The second location is south of Yankee Wharf, where several Aeonium hybrids were also scattered everywhere, at least three distinct forms with haworthii and undulatum parentage, mostly smaller plants and surprisingly many plantlets, some of them almost stemless and bearing only 2 cm wide rosettes. I haven’t seen any plants with flower remnants (this site must have been also checked in the past) but the large number of apparently young plants makes me think that seed was dispersed here at some stage. I think it is unlikely that only vegetative means of dispersal may have produced that many plantlets not to speak of the variety of forms. However, I couldn’t find here the true species Aeonium haworthii and Aeonium undulatum. In this last location plants were growing in a very composite mixture, along other naturalized succulent plants and, although very numerous, didn’t form a compact colony.


All the plants seen by me were growing directly on the lava blocks, with no substrate whatsoever, skillfully colonizing the smallest crevice of the lava fields for their advantage. Most of the plants are hanging on steep low cliffs, usually 3 – 4 m high, in some places even lower, or on rough lava blocks more or less close to the water. There is practically no soil here, just the exposed lava blocks barely covered with lichens and debris. Some plants are quite close to the high tide mark; some grow on higher ground near the coastal trail or even on the other side of the trail at the margins of the bush. Few plants might get some shade here but most of them are being exposed to full sun.


Bryophyllum delagoense (Ecklon & Zeyher) Schinz 1900. Although the first field collection was made in 1971 by A. E. Esler the name was not published until the volume 4 of Flora of New Zealand came out (Webb, C. J. & al., 1988), reinforced by the introduction on the 1989 checklist (Webb, C. J. & al., 1989)... and this is actually all I know about this plant!


Bryophyllum daigremontianum (Raymond-Hamet & Perrier) A. Berger 1930 has been recorded in 1996 as a casual occurrence on the neighbouring Motutapu Island (collected by P.J. de Lange in 1995), but reportedly present in small numbers also in Rangitoto, near Yankee Wharf. However, Craig J. Miller (1994) and Wotherspoon & Wotherspoon (2003) mention this plant, but they ignore all other Bryophyllum spp. I haven’t seen this plant (or any other Bryophyllum) in Rangitoto.


Bryophyllum pinnatum (Lamaire) Oken 1841 has been originally recorded by W.R. Sykes in 1977 in Kermadec Islands, and later on in Rangitoto and other Hauraki Gulf islands. The air plant by its vernacular name comes from tropical Asia and prefers “open scrub on sandy soil, rock crevices and outcrops.” D.R. Given (1984).   


Bryophyllum ‘Houghtonii’ Hort. (4). Andrea Julian (1992) makes this surprising reference and (apart from the variation from the name formation standards) I have to say this is a trustworthy account. Her PhD paper is extremely accurate in detail and very well documented; her statement could have been based either on W.R. Sykes (1992) referred in her paper, but which, unfortunately, I couldn’t consult directly, or on her direct studies of vegetation expansion on the lava fields. According to Julian “Bryophyllum ‘Houghtonii’ (…) is found around Yankee Wharf (…). This plant reproduces vegetatively and is one of the few exotic species which appears to be able to survive on the open aa flows.” Her account points to a significant presence posing a real danger. However, the first botanical reference was made few years later by C.J. Webb & al. (1995) and tells us a different story – apparently very rare (or a casual occurrence I would say), growing on open slopes and old lava rubble. No inflorescence of this plant has been observed, but this doesn’t mean anything as vegetative propagation is its specialty.


No environmental paper places this hybrid at Yankee Wharf or any other Rangitoto location, needless to say that I also haven’t seen any. However, it is interesting that Julian has mentioned this plant well before botanical papers have published the name. Another remark – as at that time (early to mid 1990’s) there was no effective weed control on Rangitoto and conservation work programmes were in their initial stages it looks a bit surprisingly that from a potential threat Bryophyllum ‘Houghtonii’ becomes quite a rarity, unless there was a natural decline of this plant botanists have failed to observe.


Crassula coccinea Linnaeus 1753 is another forgotten favourite of the old fashioned cottage gardens, waking up for a new glorious life here in Rangitoto. It is thought to have been naturalized in New Zealand prior to 1959 and was referred to Rangitoto by D.R. Given (1984) based on a 1982 collection made by W.R. Sykes. Crassula coccinea, with its bright red inflorescences of long tubular flowers catching your attention from the distance in late spring to high summer is actually a very interesting plant. Rudolph Marloth, the author of Flora of South Africa (1913 – 1932), writes: “This dazzling brightness of the flower is principally due to the dome-shaped form of the epidermal cells, each acting like a combination of a convex lens with a concave reflector.”  There are just few plants scattered here and there, some plantlets as well, especially near abandoned gardens near Rangitoto wharf, Gardiners Gap, Islington Bay and Yankee Wharf. It does very well in gardens in rich soil but as all succulent plants here it has to grow on lava blocks and take full advantage of any moisture or organic matter (mostly debris) accumulated in fissures and pockets – and it does it very well, as a true skilled survivor. I have no information on the propagation of this plant in Rangitoto but I suspect that vegetative means of dispersal would be the most effective. However, I have noticed here and there plantlets emerging from the remainders of withered old plants lying on the ground. Crassula coccinea has a low dynamic and is probably easy to check and therefore just a 3rd Class priority plant with Zero Density Control target set for the time being (Wotherspoon & Wotherspoon, 2003). In Miller, Craig J. & al. (1994) it is even mentioned even twice as a public enemy, the second time as Rochea coccinea.  


Crassula multicava ssp. multicava Lemaire 1862 is probably the worst succulent pest occurring in New Zealand. It was mentioned in botanical literature for the first time in 1959, but there is a strong belief that it has been naturalized much earlier in several parts of the country, probably even in the very early 20th century. Although seed hasn’t been observed in New Zealand plants, possibly due to clonal propagation in the early years of cultivation, Crassula multicava retains its high invasive potential because of the tiny plantlets formed in the axils of the inflorescence peduncles which can easily become airborne.  In Rangitoto it is by far the most spread succulent adventive plant,  being present in large numbers especially from Gardiners Gap down to Islington Bay and further south to Yankee Wharf on the eastern coast of the island and pretty much everywhere around Rangitoto wharf and the neighbouring baches in the south. Plants in their many thousands are scattered in the affected areas, from very small plants just becoming established (most of them) to large mounds up to 100 cm wide. It grows in full sun, it grows in shade, on bare lava blocks or hidden between higher plants where accumulations of organic soil have started to form, it grows everywhere, even in debris of dead vegetation, and forms well sized populations especially nearby abandoned gardens. The biggest problem with this plant is that if unchecked it can form dense mats of impenetrable vegetation preventing the natural regeneration of native ground covers. No wonder that the ultimate goal set for this plant is Eradication.


Unfortunately this extremely invasive plant managed to find its way in the inner parts of Rangitoto. Until recently I was rather under the impression that generally the naturalized succulent plants won’t be able to infiltrate – at least in a predicable future – the inner parts of Rangitoto (this being the main area of interest for the scientists) but will rather stick to a narrow coastal strip. However, in August 2009 I was able to find two spots where few plantlets of Crassula multicava have started to establish – the first one halfway on the southern Summit Track and the second one further up halfway between Wilson’s Park and the actual summit, on the north looping track. Ironically in this last location a couple of plantlets were growing in a shaded and semi-sheltered area where conservation workers have deposited barrels with herbicides (5). This clearly states that this plant can pose a real danger even in compact native vegetation.


Crassula orbicularis Linnaeus 1753 is a very popular plant here in New Zealand, but often with a mistaken identity. It used to be reportedly sold in the past in Garden Centers under different names, such as Crassula rosularis Haworth or even Aeonium haworthii hybrids, and masquerading in collections under these names for decades. It was discovered in Rangitoto just recently in 2005, few isolated plants persisting in the proximity of an abandoned quarry. As it was considered to have a high invasive potential (prolific seed production and high germination rate combined with a very effective vegetative propagation via stolons) it ended up being immediately blacklisted. Radical action was taken and all plants were removed. In 2006 when the site was revisited no other plants were found. As this plant appears to be very sensitive even to the lightest frost it probably wouldn’t have had any survival chance on a long run anyway. Even at this latitude and with the mild winters tempered by the Pacific Ocean it is very unlikely that plants like Crassula orbicularis can survive unassisted.


Crassula sarmentosa Harvey 1862 is another relatively new addition to the list, and it would be probably safe to say that it is just a casual occurrence. It was first collected by P.J. de Lange in 1995 from a slipway and published the same year in C.J. Webb’s checklist. At that time it was the only recorded location in New Zealand, but it has been collected also from Ranganui Harbour (Northland) since and thought to be a garden discard on a road bank.


Crassula tetragona ssp. robusta (Tölken) Tölken 1975 (6) has been mentioned as a naturalized plant for the first time in 1959 and is considered to occur nowadays throughout New Zealand. The Rangitoto population from Yankee Wharf is much localized but knows a very high density of plants. Yankee Wharf is definitely a play ground for invasive plants – I couldn’t believe my eyes when I first saw the dense layer of seedlings and young plants covering some areas. The word thickets would be a totally adequate description if we disregard the height of these plantlets. It usually forms compact patches and appears not to enjoy mixing with other species. With several flowering plants in the area it is very probably seed that keeps the numbers up.  On the other hand – it is this kind of substrate offered by Rangitoto that boosts its growth; you can see it in cultivation – plant a Crassula tetragona up on a pile of rocks or in a crack of a stone wall and it will thrive like nowhere else. From all succulent plants growing wild in Rangitoto, probably Crassula tetragona ssp. robusta is the most adapted for this kind of lava rubble it is growing on.


Echeveria ‘Set-Oliver’ Walther 1937 has an uncertain status. There is no botanic collection formally identifying this plant on Rangitoto Island but there is a strong belief among few enthusiasts and botanists alike that this plant is (or was?) present here as a garden escape. As this old garden hybrid used to be extremely popular here in New Zealand I find it throughout possible. There is at least one formally unidentified collection (but presumably Echeveria ‘Set-Oliver’) dating back to the early ‘70s made by A.E. Esler in Rangitoto; however, as herbarium specimens of succulent plants are not exactly the best material to support identification we will probably never know for sure.  I am pretty confident in saying that it has been cultivated here – it was extremely popular in Auckland gardens few decades ago, why wouldn’t it have been in the rock gardens nearby the holiday baches of the same Aucklanders? It does not set viable seed, so we have to look at vegetative propagation. It propagates readily from cuttings; the only problem I have found is that some organs able to assure propagation more likely in unassisted situations (i.e. detached leaves or bracts) are somewhat prone to fungal attacks and even in controlled cultivation I couldn’t get the same good results as with other similar plants. I think that Echeveria ‘Set-Oliver’ could have escaped cultivation in Rangitoto, but I give the plant low survival chances considering the limited propagation means available and the thorough vegetation checks performed especially in the last 20 years. It is not exactly persistent either as older plants become in my experience less and less energetic in time.


Echeveria multicaulis Rose 1905 is known from a single W.R. Sykes 1989 collection in Rangitoto and was first mentioned by the same in 1992. The specimen was collected from lava rubble near a demolished house site near Islington Bay and was one on the very few plants present on site. I know very well that particular area and there are at least two or three demolished dwellings in the area which could fit the very scarce description. I have spent two hours in January 2008, and came back for shorter periods of time in January 2009 and August 2009, scanning the sites thoroughly but – despite discovering few other very interesting cultivation relics – I couldn’t find anything else.    


Echeveria secunda W. B. Booth 1838 (and / or Echeveria elegans Rose 1905?) is still very common in cultivation, in pots, patios and gardens, and especially useful for borders or rock walls and banks. It was mentioned for the first time in 1959 as being naturalized in one location Canterbury (South Island), later on being recorded also in Rangitoto. It freely produces offsets and on occasion these may become established outside the gardens; however, I don’t see this plant becoming – despite its prolificacy - more than a colourful addition to New Zealand’s natural habitats. C. J. Webb & al. (1988) question however the name suggesting that collected material could very likely belong to one of its subspecies very common in cultivation. However, their short statement is stunning and (for me at least) unintelligible: “Many cultivated plants correspond to var. elegans (Baker) Otto, which has larger and more glaucous leaves, but it is impossible to ascertain whether or not any dried specimens represent this var.”


As far as I am concerned – there is no Echeveria secunda var. elegans (Baker) Otto! I wonder if the authors mean Echeveria stolonifera (Baker) Otto 1873.  Or did they mean Echeveria elegans Rose 1905 which, even if not a variety of Echeveria secunda, has indeed “larger and more glaucous leaves”? Echeveria elegans would be a very good candidate considering both aspect and extreme popularity among gardeners especially few decades back.


Echeveria setosa Rose & Purpus 1910 is also known from a single W.R. Sykes 1990 collection and was published in his 1992 article. This is also obvious just another cultivation relict having probably very low chances to survive on the long run. This time it was an old house site near Rangitoto wharf, where also few other plants were present. This is actually nearby the ferry landing point but I have to admit I haven’t covered this area too well as I always had – to my defence – other targets set for the day across the island or in the summit area. I’d like to find the time some day for the southern parts of the island.


Sedum acre Linnaeus 1753 is probably the one of the most common succulent naturalized plant here in New Zealand especially in Auckland area, being recorded as a garden escape for the first time in 1904. Webb, C. J. & al. (1988) consider this is the most widespread stone crop on both major islands; however, Flora of New Zealand, Vol. 4 (1988) does not mention this plant in Rangitoto, neither do Wotherspoon & Wotherspoon (2003), but D.R. Given (1984) and Craig J. Miller & al. (1994) do. I have not seen it in Rangitoto but with the preferred situations being “coastal cliffs, behind beaches, (…) generally on gravel, shingle, sand, rocks” (D.R. Given, 1984) the island looks like a perfect match for its needs. Unlike most of New Zealand naturalized Sedum species, Sedum acre is a prolific seeder (Webb, C. J. & al., 1988) which might have decisively contributed to its success.


Sedum album Linnaeus 1753 has been first recorded as a naturalized plant in New Zealand in 1959, but I think again that it must have been already widespread throughout the country much earlier. It is not very choosy, it thrives on all types of substrates - “roadsides, railways, waste places, banks, rock walls, hillside slopes near gardens, riverbeds, especially prolific on dry shingle, gravel, lava and other volcanic rock, sometimes on sand and sandstone” (Webb, C. J. & al. 1988) if kept on the dry side.  It used to be widely cultivated, becoming unfortunately in time a nuisance in most of the gardens (mine including) because it propagates very profusely. It is a kind of garden weed in the end, extremely hard (or even impossible) to eradicate without a disproportionate effort from rocky places, walls or along the foot paths and “is so prolific that it has a tendency to smother slower-growing plants” (Webb, C. J. & al. 1988). I am not sure if New Zealand plants set seed or not, however, unassisted vegetative propagation is no problem at all. It might be very variable in its appearance (especially leaf size and stem height) due to specific conditions, but still hard to mistake for other stone crops, especially when in flower.


Sedum album is very common in Rangitoto, occurring mostly around former baches and abandoned gardens, in most of the cases not directly on the lava blocks, contrary to C.J. Webb’s account, but in such places where a thin layer of sand or shingle mixed with crushed shells is available. I think that the black basaltic lava blocks get too hot in summer for this plant. However, due to excessive sunlight, heat and water stress the leaves in most of the plants seen by me here are nicely bronze coloured – a colour that I have never managed to get in my rock garden! It forms more or less isolated patches of vegetation along the eastern coast from Gardiners Gap down to Islington Bay and further south to Yankee Wharf and reportedly also in the southern parts around Rangitoto wharf. In extreme hot and dry years it dies almost completely off in high summer only to regenerate from its remainders with the first cooler nights of the late summer or early autumn when dew is available in the first hours of the morning. None of the two major environmental papers referred here mentions this very invasive plant in Rangitoto, but I assume that Sedum mexicanum is just a kind of generic name used for all stone crops in Wotherspoon & Wotherspoon (2003). If so, Eradication would be the ultimate goal to achieve, although I highly doubt that it could be achieved without a sustained human and financial effort.


Sedum forsterianum C. A. Smith 1808 has been mistaken a long time for Sedum reflexum (Webb, C. J. & al. 1988) in all its North Island localities and this raises a question – shall we discard all previous Rangitoto references of the latter? According to heir 1988 work Sedum forsterianum is scattered in several localities in Auckland area, including Hauraki Gulf islands such as Rangitoto and Little Barrier, being actually collected for the first time (and positively determined as Sedum forsterianum) (7) by Beaver back in 1978. “S. forsterianum appears to be confined to the north of the North Id. It has been confused with S. reflexum in N.Z. partly because the important distinguishing character of lf shape as seen in cross section is only evident in living material; consequently, some herbarium specimens of wild plants cannot be confidently assigned to either sp. S. forsteranum is usually a somewhat smaller and more slender plant than S. reflexum, the flowers also seem to be slightly smaller, and the dense cone-like appearance of the ascending leafy shoots is characteristic.”  And a very interesting detail: “N.Z. plants of S. fosterianum generally agree with descriptions in overseas works but differ in retaining almost no dead leaves beneath the leaf clusters.” Apart from this – “S. forsterianum has until recently usually been treated as a var. or forma of S. rupestre L. Thus, in many older works S. rupestre sens. strict. was said to have glaucous leaves and var. or f. forsteranum green leaves.”


There is little I actually know about these two plants; however, I have not seen any plant which could have been one or the other. It is true that my main focus was on the coastal cliffs and lava fields and less on the abandoned gardens – with few specific exceptions. But by being – that’s my understanding - somewhat less invasive compared to other stone crops it would make probably sense to browse particularly these places. Well, that’s a target for the next trip.

 

Sedum mexicanum Britton 1899 is mentioned for the first time by D.R. Given (1984) as a casual occurrence based on a 1966 A.J. Healy collection in Heathcote – Christchurch (Southern Island). No other references over the years, let alone Rangitoto. However, this name pops up now very surprisingly in Wotherspoon & Wotherspoon (2003) as a Class 3 priority targeted for Eradication. I haven’t seen it and I also couldn’t find any reference in botanical literature or environmental papers.


Sedum praealtum ssp. praealtum De Candolle 1847 (mentioned in Webb, C. J. & al. 1988) does not form large groups either, but rather scattered plants are seeking shade and shelter. One of the things I have noticed – these plants do not occur usually in open spaces, but elsewhere where stronger plants have already established, in most of the cases at bush margins, and sometimes almost hidden between Agapanthus tussocks – very abundant especially in Yankee Wharf – or anywhere where accumulations of vegetation debris may occur. I think there could be two good reasons for this – moisture is retained a little bit longer and the black basaltic lava blocks do not overheat when covered with vegetation debris. There are mostly medium sized plants and just very few plantlets pointing towards a limited vegetative reproduction. It looks to be a shy flowerer - I have seen several times this plant during past trips in Rangitoto, all along the eastern coast from Gardiners Gap to Yankee Wharf, but only during the last one I saw a couple of flowering specimens.


Sedum reflexum Linnaeus 1753. D.R. Given (1984) places this plant in Rangitoto while C.J. Webb (1988, 1989) takes a step back and reveals the long time confusion with Sedum forsterianum. Apart from this – there is a certain variability of this plant, regarding colour, height and even habit induced by different types of climate; however, there is little value in all this information unless you see the two plants next to each other. C.J. Webb & al. (1988): “Typical wild South Island S. reflexum has erect sterile shoots with the leaves crowded along their length and not confined in a terminal tuft, and the leaves are glaucous, narrow, and subterete with rounded surfaces (broadly elliptic in transverse section). Generally, S. reflexum seems to be a larger and more erect plant than S. forsterianum but this character is of very limited value unless the two spp. are growing together.”


Except for Mt. Albert (Auckland) and Wellington all other locations of Sedum reflexum are in the South Island as this plant seems to prefer cooler situations. Although C.J. Webb is not explicit about Rangitoto plants in particular I think it would be wise for us to regard all previous records as doubtful.

 

 

References:


Allen, H. H. 1961: Flora of New Zealand, Vol. 1 (The updated electronic version, Vol. 1, 2004 - http://floraseries.landcareresearch.co.nz );


Auckland Regional Council 2002: Pest Management Strategy 2002 – 2007 (August 2002) – co-ordinated by Gwen Bull & Bill Burrill;


Given, D.R. 1984: Checklist of dicotyledons naturalized in New Zealand – 17. Crassulaceae, Escalloniaceae, Philadelphaceae, Grossulariaceae, Limnanthceae (New Zealand Journal of Botany, Vol. 22);


Heenan, P.B. & al. 2002: Checklist of dicotyledons, gymnosperms and pteridophytes naturalized or casual in New Zealand: Additional Records 1999 - 2000 (New Zealand Journal of Botany, Vol. 40);


Julian, Andrea 1992: The vegetation pattern of Rangitoto (unpublished PhD thesis);


Miller, Craig J. & al. 1994 – ARK2020: a Conservation Vision for Rangitoto and Motutapu Islands (Journal of The Royal Society of New Zealand, Vol. 24);


New Zealand Plant Conservation Network (2005 - 2010) (www.nzpcn.org.nz );


Sykes, W.R. 1992:  Succulent plants of Rangitoto (in Auckland Botanical Society Journal) (not directly consulted);


Webb, C. J. & al. 1988: Flora of New Zealand, Vol. 4 (The updated electronic version, Vol. 4, 2004 - http://floraseries.landcareresearch.co.nz );


Webb, C.J. 1989: Checklist of dicotyledons, gymnosperms and pteridophytes naturalized in New Zealand: additional records and corrections (New Zealand Journal of Botany, Vol. 27);


Webb, C.J. & al. 1995: Checklist of dicotyledons, gymnosperms and pteridophytes naturalized in New Zealand: additional records 1988 - 1993 (New Zealand Journal of Botany, Vol. 33);


Webb, C.J. & al. 1999: Checklist of dicotyledons, gymnosperms and pteridophytes naturalized or casual in New Zealand: Additional Records 1988 - 1993 (New Zealand Journal of Botany, Vol. 37);


Wotherspoon,  S.H. & Wotherspoon, J.A. 2003: The Evolution and Execution of a Plan for Invasive Weed Eradication and Control, Rangitoto Island, Hauraki Gulf, New Zealand;

Zimer, Eduart 2007: Plante suculente naturalizate in Noua Zeelanda (on www.aztekium.ro);

Zimer, Eduart 2008: Succulent plants from down under – Adventive Plants (Part 4) – X. A brief overview of the adventive succulent flora of Rangitoto Island (http://eduart.page.tl);


Zimer, Eduart 2008: The naturalized Aeonium of Rangitoto Island (Hauraki Gulf, New Zealand) – on International Crassulaceae Network (ICN) www.crassulaceae.net; Romanian versions also available on www.cactusi.com  and www.aztekium.ro;


Zimer, Eduart 2009: Aeonium of Rangitoto (in New Zealand Cactus and Succulent Journal, Vol. 62, No. 2);


Zimer, Eduart 2009: The succulent corner at Yankee Wharf, Rangitoto Island (in New Zealand Cactus and Succulent Journal, Vol. 62, No. 4);


Zimer, Eduart 2009: A new Aeonium natural hybrid in New Zealand? (Notes on Aeonium ‘Rangitoto’ - I) (In print  in New Zealand Cactus and Succulent Journal, 2010, and in the e-magazine Avonia-News 2009:11, December 2009);

Zimer, Eduart 2009: The fragile boundary between conservation and destruction on Rangitoto Island, Hauraki Gulf, New Zealand - Part 1 (http://eduart.page.tl);

Zimer, Eduart 2010: The fragile boundary between conservation and destruction on Rangitoto Island, Hauraki Gulf, New Zealand - Part 2 (due on http://eduart.page.tl by mid 2010).

 

Further readings:

 

Timmins, S.M.  & Braithwaite, H. ca. 2002: Early Detection of Invasive Weeds on Islands.

 

My Notes:


(1)    The Metrosideros bush covers over 57% of the island (Andrea Julian, 1992).

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(2)    Aloe maculata, Aloe arborescens, Agave americana and the yellow flowering form of Carpobrotus edulis.

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(3)    It is actually amazing to note the significant gap that exists between botanical accounts and the reality in the field in some instances. In some cases botanical accounts rely on studies made 10 – 20 – 30 years ago and every new account repeats things already known for some time but which might be not true to the reality anymore. In most of the cases any account that is not based on collected herbarium specimens is largely disregarded. It is not uncommon that amateurs have a better knowledge of the field. On the other hand environmental papers are much more accurate being based mostly on current field work but generally show a lower interest for botanical subtleties when referring to exotic species. E.g. there is no botanical account placing Aeonium haworthii (or its hybrids) on Rangitoto; a very serious environmental paper (Wotherspoon, S.H. & Wotherspoon, J.A. 2003) indirectly considers (by omission?) that all Rangitoto plants are Aeonium haworthii, none of them being true.

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(4)    This plant was later referred by New Zealand authors as Bryophyllum daigremontianum x Bryophyllum delagoense, Bryophyllum ‘Houghton’s Hybrid’ and Kalanchoe daigremontiana x Kalanchoe tubiflora.

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(5)    Conservation work – no matter the efforts or quality – does not grant anything. There are a few well known cases when infested materials, equipment or tools have contributed to the introduction of pests.  

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(6)    New Zealand botanists refer this plant always as Crassula tetragona L., however, Tölken considers that New Zealand wild plants have to be assigned to ssp. robusta.

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(7)    There are two orthographic versions of this name – forsterianum and forsteranum. Both variants of the name are inconsistently used by different New Zealand authors (even in Flora of New Zealand series). I have preferred to use the first name as this was used by Ray Stephenson, who is the ultimate contemporary Sedum authority.

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Eduart Zimer, January - February 2010


http://eduart.page.tl/Home.htm

Photos

1.  Typical light bush vegetation of the basaltic lava fields on the track to Wreck Bay / Boulder Bay halfway between the shore and Islington Bay Road. Note the lichens still thriving on the ground.

2. Trichomanes reniforme is despite its aspect a true fern. It is also a sub-succulent plant, having a certain ability to store moisture in its translucent leaves. During periods of draught it uses it up and then the leaves get in a papery state only to come to new life when moisture becomes freely available. 

3. The main cone of Rangitoto, with Metrosideros excelsa in the foreground.  The scoria cones have very composite scrub vegetation mix… 

4. …but also patches with the appearance of a light bush. A particular feature – the deeper soil-like substrate.


5. The shores are less vegetated, sometimes almost barren, as this lava flow at Wreck Bay, in the northern part of Rangitoto. Halophyte grasses and generally xerophytes have better chances here. 

6. A mound of Sarcocornia quinqueflora ssp. quinqueflora growing in the splash zone close to Yankee Wharf.

7. A mix of succulent plants and Agapanthus praecox ssp. orientalis – very invasive and present in large numbers in some places – at Yankee Wharf, where the bush does not come down to the waterline.

8. The gardens of the abandoned baches is the source of all Crassulaceae escaped on the island.

9. The Aeonium colony at Islington Bay, before being destroyed by the Department of Conservation.

10.  A glorious Aeonium undulatum emerging from a long summer dormancy in the Islington Bay colony.  There is virtually no soil here, just vegetal debris (acting as moisture retainer) and a crust of lichens (ultimately fixing nitrates for higher vascular plants). 

 

11. This is Aeonium ‘Rangitoto’, one of the very few more or less adult plants seen here at Islington Bay, presumably an Aeonium undulatum x haworthii backcrossed to Aeonium haworthii.

12. One of the presumed parents of the above plant – Aeonium haworthii, a form which looks pretty much alike the true species. This plant used to be fairly common in the Aeonium colony of Islington Bay before being checked by the Department of Conservation, but not occurring in big numbers.   

13. This is the other parent… Aeonium undulatum x haworthii, from the same Islington Bay colony.   

14.  An uncertain Aeonium in late winter near Islington Bay. Judging by the mosses established here this east facing plant has found a rather moist spot. 

15.  Several haworthii blooded Aeonium plants growing in the small crevices of the basaltic lava blocks at Yankee Wharf.

16.  A Yankee Wharf Aeonium competing with Aloe maculata for the moisture of the fissures and crevices of the lava blocks.

17. A branching Aeonium haworthii in Islington Bay.

18.  Crassula coccinea - the “dazzling brightness” of the thyrse gives always problems when trying to take a picture – you’ll never get it right! This picture was taken at Yankee Wharf.

19.  Another Crassula coccinea from Yankee Wharf with Crassula multicava plantlets in the background.

20.  Crassula coccinea, young plants emerging from damaged stems.

21. An extra-large mound of Crassula multicava (around 150 cm wide) at the entrance of a former dwelling. Note the cress-cross of peduncles releasing many hundreds of tiny but invasive plantlets. 

22. Crassula multicava at Rangitoto wharf, relatively close to former human settlements. The plant in the right is Griselinia lucida, a native shrub. 

23.  A beautiful specimen of Crassula multicava at Yankee Wharf.

24.  A very exposed Crassula multicava close to the Rangitoto wharf, in the southern parts of Rangitoto. 

25.  Nothing short of a miracle – a young Crassula tetragona ssp. robusta emerging from a fissure of a lava block at Yankee Wharf. 

26. Crassula tetragona ssp. robusta has a much localized distribution on Rangitoto, but it occurs in large numbers.

27. The site south of Yankee Wharf - with Motutapu Island beyond the shallow waters of the channel – is a true heaven for the adventives Crassulaceae. However, you can see the predominance of the white flowering Agapanthus praecox ssp. orientalis in this area – a very invasive plant almost out of control.

28. Few abandoned baches close to Islington Bay wharf. I spent at least two hours with my younger son Vlad, my usual companion during the Rangitoto trips, scanning the entire area in search of Echeveria multicaulis and other cultivation relics.

29. Sedum album in winter, at Islington Bay wharf...

30.  … and in high summer south of Yankee wharf. It is very common in Rangitoto, occurring mostly around former baches and abandoned gardens, where a thin layer of sand or shingle mixed with crushed shells s available.


31. Two young Sedum praealtum ssp. praealtum emerging from vegetation debris halfway between Islington Bay wharf and Yankee Wharf.

32 - 34. Sedum praealtum ssp. praealtum seems to be a shy flowerer; however, it is a delightful plant even when not in flower.

35. A composite mix of naturalized plants at Yankee Wharf – Crassula coccinea, Agapanthus praecox ssp. orientalis,   Crassula tetragona ssp. robusta and Aloe maculata – within few meters.

36.  Rangitoto Island seen from Northcote – Devonport.

 

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