Plant spinescence in alpine Australia, part 1: the mainland

 (writing in progress)
 
The high-altitude area of Australia (https://en.wikipedia.org/wiki/Australian_Alps and https://en.wikipedia.org/wiki/Alpine_vegetation_of_Tasmania) is small compared to that of New Zealand, lying at relatively low altitudes and latitudes.

Hence spinescent elements in alpine vegetation may be more easily overlooked in Australia than in New Zealand.

So, I was curious to see which species in the alpine flora of Australia qualify as spinescent, and whether any vegetation types have spinescent spp. as dominants.
 
First I deal with the mainland.  My sources here are Costin et al. (1979) and Codd et al. (1998). In a subsequent Post, I will deal with Tasmania.
 
The shrub Melicytus dentatus (Violaceae, https://www.inaturalist.org/taxa/537927-Melicytus-dentatus) is nodal-spinescent. It persists into the alpine zone (above the treeline) as prostrate shrubs, often located at the bases of rocks.

All the other spp. listed below are in the category of foliar, not nodal, spinescence.
 
There are two spp. of grasses qualifying as weakly or marginally foliar-spinescent: Rytidosperma alpicola (https://www.inaturalist.org/taxa/870090-Rytidosperma-alpicola) and R. nudiflorum (https://www.inaturalist.org/taxa/323456-Rytidosperma-nudiflorum).

Both tend to be dominant in their herbaceous vegetation types (above the treeline), the first type being in crevices and on ledges of crags and large rock outcrops, the second type being sod tussock grassland.
 
There are few spp. of Acacia in mainland alpine Australia, and none above the treeline. However, one subalpine sp., a small shrub, is certainly foliar-spinescent: Acacia siculiformis (https://www.inaturalist.org/taxa/567724-Acacia-siculiformis).
 
Colobanthus pulvinatus (Caryophyllaceae, https://www.inaturalist.org/taxa/894795-Colobanthus-pulvinatus) seems to qualify as foliar-spinescent. It is a cushion plant sometimes described as ‘prickly’. This genus is shared with New Zealand, where C. canaliculatus (https://www.inaturalist.org/taxa/407296-Colobanthus-canaliculatus) and C. hookeri (https://www.inaturalist.org/taxa/400981-Colobanthus-hookeri)*are particularly closely related and so might, possibly, also be foliar-spinescent.
 
The erica Richea continentis (https://www.inaturalist.org/taxa/541637-Richea-continentis), growing in alpine bogs, is foliar-spinescent.
 
The erica Epacris paludosa (https://www.inaturalist.org/taxa/541635-Epacris-paludosa), growing in alpine bogs, is foliar-spinescent; and its congener E. microphylla (https://www.inaturalist.org/taxa/321118-Epacris-microphylla) is at least weakly foliar-spinescent.
 
Because R. continentis and E. paludosa sometimes grow together in ‘raised bogs’, there may be small areas of vegetation dominated by these (weakly) foliar-spinescent plants.
 
The following spp. are ‘disappointments’, having names suggestive of spinescence, or close relatives elswhere that as spinescent, but turning out not to be spinescent in mainland alpine Australia.
 
Several other grasses in mainland alpine Australia seem to have the makings for foliar spinescence, possessing both relatively rigid leaves and sharp tips to the leaves. However, none quite makes the grade.
 
Poa costiniana (https://www.inaturalist.org/taxa/1205890-Poa-costiniana) is called ‘prickly snow grass’, but the name ‘prickly’ seems to be an exaggeration. It is the ‘coarsest grass above the snowline’, but its leaves are not described as having ‘pungent’ tips. Poa labillardierei var. labillardierei (https://www.inaturalist.org/taxa/323470-Poa-labillardierei) has leaves described as ‘sometimes ending in a prickly point’. However, I do not accept it as spinescent, and it does not seem to reach the alpine zone.
 
‘Prickly woodruff’, Asperula scoparia (https://www.inaturalist.org/taxa/801695-Asperula-scoparia), has spinescence only on its fruits.
 
The genus Aciphylla (https://www.inaturalist.org/observations?taxon_id=349792), which attains spinescence in New Zealand, is present in mainland alpine Australia. However, it is non-spinescent here. Aciphylla is a genus which, like Podocarpus (https://www.inaturalist.org/observations?taxon_id=85284) and Olearia (https://www.inaturalist.org/observations?taxon_id=129177), attains greater spinescence in New Zealand than in Australia.
 
My commentary:
 
We can look at the incidence of spinescence, particularly foliar spinescence, in mainland alpine Australia from a ‘half-empty’ or a ‘half-full’ perspective.
 
In the ‘half-empty’ perspective, this ecological zone seems never quite to hit the mark, mainly because those spp. with spinescent leaves are only just ‘prickly’, and in several cases less prickly than congeners farther afield. The foliar spinescence in mainland alpine Australia seems rather ‘half-hearted’. The genus Aciphylla seems particularly so, relative to New Zealand.
 
However, from the ‘half-full’ perspective, I note the following.
 
Firstly:
Several of the above spp. do get close to dominating the vegetation in which they occur (albeit in only small areas at a time).
 
Secondly:
The foliar spinescence of Epacris remains noteworthy given that this genus is the closest thing to a southern counterpart for Erica of Africa and Eurasia, a genus which nowhere attains spinescence despite being extremely speciose.

Nobody with extensive experience of ericas in Europe or southern Africa would dream of a foliar-spinescent erica. Yet not only are many ericas in Australia foliar-spinescent, but even the genus most closely ‘mirroring’ Erica in most ways, namely Epacris, attains foliar-spinescence (albeit rather weakly in the alpine ecosystem).
 
Thirdly:
The genus Rytidosperma extends to southern South America, Indonesia, and the Pacific, but it seems to be foliar-spinescent only in Australia. If so, I find this noteworthy, particularly because the closely related genus Danthonia (taking the place of Rytidosperma in e.g. Eurasia and North America) is, as far as I know, always non-spinescent.
 
 Costin et al. (1979), page 135, describe Poa costiniana, as having leaves ‘rather rigid and pungent’. Since the first author is the one after whom this plant has been named, I guess he is a reliable source. Poa costiniana ‘is the main dominant in sod tussock grassland.’ Sod tussock grassland also contains the weakly foliar-spinescent Rytidosperma nudiflora. Another species in the area, Poa fawcettiae, is also described by these authors as ‘moderately stiff and pungent-pointed’, thus qualifying as marginally foliar-spinescent. So, on second thoughts, we can add Poa costiniana to the list of (weakly) foliar-spinescent grasses in mainland alpine Australia and it tends to dominate a vegetation type, namely sod tussock grassland, over small areas.

Further confirmation comes from Kirkpatrick (1197), page 132, who states that Poa costiniana ‘is a much coarser grass than P. fawcettiae; also similar to [Tasmanian] P. gunnii, which has leaves that are pointed, but not prickly’.

The name ‘prickly snow grass’ does, after all, seem apt for P. costiniana.

Do any ‘alpine’ areas elswhere on Earth have a common tussock grass, in boggy sites along drainage lines, that is at least weakly foliar-spinescent? What about New Zealand? And if not, why not in ecological terms?

So, in corrected summary to what I wrote above, the overall result is that the following vegetation types in mainland alpine Australia come close to dominance by (weakly) foliar-spinescent species:

• sod tussock grassland, in which Poa costiniana and Rytidosperma nudiflora can dominate the community along drainage lines at the bottoms of alpine valleys, and
• raised bog, in which Richea continentis, Epacris paludosa and E. microphylla can dominate the community, which occurs as limited patches on gentle slopes.

It is interesting that both of these vegetation types, dominated by (weakly) foliar-spinescent plants, occur on poorly-drained substrates.

(writing in progress)

Posted on June 26, 2022 02:15 AM by milewski