Unusual combination of features in Ericaceae: the case of Acrotriche serrulata

It is easy for naturalists familiar with the Cape Flora (https://en.wikipedia.org/wiki/Cape_Floristic_Region) to feel that they know the ‘kingdom of the heathy ericas’ (https://botanicalsociety.org.za/diversity-unparalleled-an-introduction-to-ericas/).

However, heathy Ericaceae in Australia include some remarkable plants, of which I introduce one example here.

I refer to Acrotriche serrulata (https://www.inaturalist.org/taxa/323796-Acrotriche-serrulata and https://vicflora.rbg.vic.gov.au/flora/taxon/94ad4263-480e-4d4c-bf73-3c0b0573ff4e and https://www.yarraranges.vic.gov.au/PlantDirectory/Herbs-Groundcovers/Acrotriche-serrulata and https://www.castlemaineflora.org.au/pic/a/acrot/acser.htm and scroll in http://apswarrnambool.org.au/pdf/small%20shrubs.pdf and https://grasslands.ecolinc.vic.edu.au/fieldguide/flora/honey-pots#details).

This species is widespread in coastal New South Wales and Victoria, as well as Tasmania. It is typical of the fynbos-like understorey of 'dry sclerophyll forest' (http://www.viridans.com/ECOVEG/dry%20sclerophyll.htm and https://en.wikipedia.org/wiki/Tasmanian_dry_sclerophyll_forests and https://www.environment.nsw.gov.au/threatenedspeciesapp/VegFormation.aspx?formationName=Dry+sclerophyll+forests+(shrubby+sub-formation)).

However, it also extends to treeless heathlands. I refer to what in Western Australia would be called ‘kwongan’ (https://en.wikipedia.org/wiki/Kwongan), and what in eastern Australia is perhaps the closest thing to fynbos found on any other continent.
 
Acrotriche serrulata tends to grow as a mat-plant. It is < 30cm, and usually < 15 cm, high (https://www.inaturalist.org/observations/120616727 and https://www.inaturalist.org/observations/125153908). This seems to be associated with its pollination by ants and mammals, instead of birds (https://eprints.utas.edu.au/11811/).
 
The flowers, although full of nectar, are small and greenish (https://www.inaturalist.org/observations/91522074 and https://www.inaturalist.org/observations/94271286 and https://www.inaturalist.org/observations/83246317).

These flowers are borne low on the plant, via cauliflory (https://www.inaturalist.org/observations/90363326) - an arrangement absent from all African ericas, as far as I know.

Here we seem to have that unusual entity, a mammal-pollinated erica, with a growth-form accordingly adapted.

The phenology is odd, because A. serrulata flowers in mid-winter, at the coldest time of year.
 
Acrotriche serrulata belongs to a foliar-spinescent genus. I do not know of any African erica that has spinescent leaves.

Come to think of it, I cannot recall any other plant, worldwide, that combines foliar spinescence (https://www.inaturalist.org/observations/99189327 and https://www.inaturalist.org/observations/122443632 and https://www.inaturalist.org/observations/120799560) with pollination by mammals.
 
Unlike any African erica, Acrotriche serrulata has fleshy fruits (https://tasmanianplants.wordpress.com/2009/12/25/haveya-had-ya-heaths/). I.e. it is endozoochorous (https://en.wikipedia.org/wiki/Seed_dispersal_syndrome).

The combination of foliar spinescence with fleshy fruits - although absent from fynbos - is not particularly unusual in Australia (https://www.inaturalist.org/journal/milewski/62096-list-of-species-combining-spinescent-leaves-and-bright-hued-fleshy-fruits-in-australia#).

These drupes are unusually small for fleshy fruits, having diameter 3-4.5 mm. Nonetheless, there is fleshy fruit-pulp around a central ‘stone’. The latter is spongy but hard, and would be passed intact when Aboriginal people ate the fruits.

Even odder, the dull-hued ripe fruits, like the flowers, do not advertise themselves by means of colour, in A. serrulata.

I do not know the natural dispersers of the seeds. However, I suspect both the emu (Dromaius novaehollandiae, https://www.inaturalist.org/taxa/20504-Dromaius-novaehollandiae) and lizards, such as Tiliqua (https://www.inaturalist.org/observations?place_id=any&taxon_id=37455&view=species), to participate.

It is possible that possums such as Trichosurus (https://www.inaturalist.org/observations?place_id=any&taxon_id=42805&view=species), which pollinate the plant, also disperse and sow the seeds. If so, this would be another odd combination.
 
Apparently, germination is slow.
 
Post-fire regeneration is vegetative. Lifespan is reputed to be 5-25 years.
  
The genus Acrotriche extends to southwestern Western Australia, particularly in the mallee-heath (https://en.wikipedia.org/wiki/Mallee_bioregion and https://www.dcceew.gov.au/sites/default/files/documents/mvg14-nvis-mallee-woodlands-and-shrublands.pdf) of the southern coast. However, as far as I know, it is absent from jarrah forest (https://en.wikipedia.org/wiki/Jarrah_Forest).

Not all species in the genus (https://en.wikipedia.org/wiki/Acrotriche) are mat-plants; some grow as ‘normal’ divaricate shrubs. In some species, the ripe fruits may also be fairly bright-hued (https://en.wikipedia.org/wiki/Acrotriche#/media/File:Orange_Fruit_Norah_Head.JPG and https://www.inaturalist.org/journal/milewski/62096-list-of-species-combining-spinescent-leaves-and-bright-hued-fleshy-fruits-in-australia#).

So, A. serrulata is an extreme case within not only its family, but also its genus. 

http://davesgarden.com/guides/pf/go/57186/

https://www.anbg.gov.au/images/photo_cd/537_FAGG/DSC_4586_2.jpg

http://www.utas.edu.au/dicotkey/dicotkey/EPACRIDS/ZAcrotriche_serrulata.htm

http://www.montroseswildgarden.net/p/grasses-rushes-ferns.html

http://www.bournda-e.schools.nsw.edu.au/ecosystems/terrestrial/herbarium/images/images/Acrotricheserrulata01ac.jpg

http://www.bournda-e.schools.nsw.edu.au/ecosystems/terrestrial/herbarium/images/images/Acrotricheserrulata01bc.jpg

http://www.surfcoast.vic.gov.au/files/090259a9-fb29-45da-8e9b-9f3d0103d22f/123avot.jpg

http://natureshare.org.au/observations/53b39850e35eb1298400e83b?display=thumbnails&order_by=date&species=acrotriche_serrulata

Posted on July 22, 2022 08:02 AM by milewski