Philotheca pungens, an example of foliar spinescence in the aromatic family Rutaceae

 (writing in progress)
 
Certain lineages of plants tend to emphasise physical defence from herbivores (e.g. spines, fibrousness). Others tend to emphasise chemical defence from herbivores (noxious substances in the foliage which often smell pleasant to the human nose but presumably smell revolting to herbivores’ noses).
 
Two families which seem to rely mainly on chemical defence are Rutaceae (rues) and Lamiaceae (mints), respectively represented in the public mind by the condiments ‘lemon-peel’ and ‘mint’.

Both families are well-represented in various fire-prone vegetation types which are rich in foliar-spinescent plants.

However, neither of them tends to have the combination of sclerophylly and foliar spinescence typical of e.g. kwongan. Instead, they tend to have relatively soft leaves which give off strong smells when damaged.
 
However, there are exceptions. Two such exceptions are Philotheca pungens (https://www.inaturalist.org/taxa/958094-Philotheca-pungens) in the Rutaceae and Hemiandra pungens (https://www.inaturalist.org/taxa/545347-Hemiandra-pungens) in the Lamiaceae.

Both have traded in aromatic leaves for spinescent leaves similar to the typical leaves of e.g. ericas in Australia.

Philotheca pungens occurs in mesic to semi-arid South Australia while H. pungens is restricted to southwestern Australia.
 
The genus Philotheca contains perhaps 50 spp., and as far as I know by far the majority of these are non-spinescent.

The genus Hemiandra contains only about 7 spp. and perhaps most of them are spinescent, although I have yet to investigate them on a species-by-species basis.

Philotheca pungens grows as a low shrub whereas H. pungens grows as a shrub so low that it can be called prostrate.
 
It will be interesting to see if foliar-spinescent rues and mints have evolved on any landmass other than Australia.
 
The following is a useful source for Philotheca pungens: https://vicflora.rbg.vic.gov.au/flora/taxon/26ba361d-25f1-489e-add0-75f39bb8bea7
 
The following shows the distribution of Philotheca pungens: https://bie.ala.org.au/species/https://id.biodiversity.org.au/node/apni/2889713.
 
The following shows the ‘pungent’-tipped leaf of Philotheca pungens: https://www.inaturalist.org/observations/63724843
  
The following several photos all show the foliage of Philotheca pungens: https://www.inaturalist.org/observations/36011685 and https://www.inaturalist.org/observations/100055851 and https://vicflora.rbg.vic.gov.au/flora/taxon/26ba361d-25f1-489e-add0-75f39bb8bea7.
 
The following is a useful source for Hemiandra pungens: http://www.northqueenslandplants.com/Australian%20Plant%20Families%20G-M/Lamiaceae/Hemiandra/Hemiandra%20pungens.html
 
The following shows the distribution of Hemiandra pungens: https://florabase.dpaw.wa.gov.au/browse/profile/6839.

spinescent leaves of Hemiandra pungens:
https://www.inaturalist.org/observations/73476879 and https://www.inaturalist.org/observations/101701653

(writing in progress)

Publicado el julio 24, 2022 05:53 MAÑANA por milewski