An odd case of a leaf-spinescent grass that is also a resurrection plant

(writing in progress)

The genus Micraira (https://www.inaturalist.org/taxa/844774-Micraira-subulifolia and https://www.delta-intkey.com/grass/www/micraira.htm) contains 14 or 15 spp., restricted to tropical Australia. The habitat is rocky places in shallow soils.

Probably all the spp. are resurrection plants. And I have just read that at least two spp., namely Micraira dentata and Micraira pungens, are foliar-spinescent.
 
I have long known of graminoid, foliar-spinescent resurrection plants in the form of Borya (https://www.inaturalist.org/observations?taxon_id=370047). However, this is the first case I have come across of foliar-spinescent resurrection plants among the true grasses of the world.
 
I suspect that at least one of the ca 90 spp. of Triodia, namely Triodia wiseana (https://www.inaturalist.org/taxa/1239787-Triodia-wiseana), is also a resurrection plant, at least in the sense of being diallagous. Triodia wiseana occurs in a particularly hot part of semi-arid Australia, i.e. on stony hillslopes in the Pilbara.

Whereas most spp. of Triodia look at least dully green even in the dry season, photos of T. wiseana show that it goes fully non-green (i.e. fawn or greyish) in the dry season. Yet the leaves are so sclerophyllous, and the plant so slow-growing, that it seems unlikely that re-greening after rain is achieved mainly by the growth of new leaves. Rather, it seems likely that the main re-greening of the hummocks involves re-greening of the already existing leaves.
 
Micraira forms perennial, mat-like plants resembling overgrown moss. The habitat is on sandstone rocks, often seasonally wet. I note a similarity in growth-form and habitat with the lily Borya in mediterranean southwestern Australia, but the two groups lie on opposite sides of Australia, geographically and climatically (summer-rainfall vs winter-rainfall, tropical vs temperate).
 
I can now propose an additional syndrome to the four or five syndromes I have previously proposed w.r.t. foliar-spinescent grasses. We now have a syndrome of foliar-spinescent grasses which are resurrection plants.

If Triodia wiseana turns out not to be diallagous, then this syndrome might be nominal in the sense that it involved only two spp. worldwide, restricted to only one type of environment in one area (sandstone in Arnhem Land, which has a mesic, not arid or semi-arid, climate). However, the syndrome does exist, and it stretches our conceptual framework about the ecological functions of foliar spinescence, not so?
 
From first principles it might have been predicted that resurrection plants/diallagous plants might tend to be foliar-spinescent, based on the rationale that the more lignified the leaf, the longer-lived it can be through the seasonal cycle of hydration and dehydration.

However, in reality many resurrection plants do not have sclerophyllous leaves; and as it turns out sclerophylly and foliar spinescence are not as well-correlated as expected. There is a consistent pattern in which foliar-spinescent plants crop up as certain spp. within genera that are otherwise not foliar-spinescent. Foliar spinescence seems to have evolved on a species-by-species basis, rather than being a consistent feature within a given genus.

This applies to Micraira, which seems to have developed foliar spinescence in only two of its ca 14 spp., even though all of the 14 spp. seem to have consistent growth-form and ability to resurrect.
 
This leaves me with the impression that, in Micraira as in other genera of grasses, foliar-spinescence is mainly adaptive to herbivory rather than to climate or nutritional status. 
 
Genus Micraira in general:

The leaf of M. dentata is the one on the left of the two leaves in the following drawing. The leaf of M. pungens is that on the right of this pair. These leaves show foliar spinescence.
 
https://www.delta-intkey.com/grass/images/micrai02.gif

The following shows the NON-SPINESCENT leaves of Micraira compacta and M. subspicata for comparison. These leaves of congeners do not show foliar spinescence.
 
Micraira dentata:
http://ausgrass2.myspecies.info/content/micraira-dentata
 
Micraira dentata: https://keys.lucidcentral.org/keys/v3/AusGrass/key/AusGrass/Media/Html/MICRAIRA/MICDEN.HTML

Micraira dentata:
 
Micraira dentata:

Micraira pungens:
http://ausgrass2.myspecies.info/content/micraira-pungens
 
Micraira pungens: https://keys.lucidcentral.org/keys/v3/AusGrass/key/AusGrass/Media/Html/MICRAIRA/MICPUN.HTML
 
Micraira pungens: https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:408439-1

(writing in progress)

Publicado el junio 20, 2022 08:14 MAÑANA por milewski