Succulent plants in Australia are few, but some grow taller than expected

@arthur_chapman Hi Arthur, Could you please check that I have not made any mistakes in this Post? with many thanks, from Antoni

Australia is the continent poorest in perennial plants with succulent foliage.

The indigenous flora of succulent shrubs in Australia is restricted. It consists mainly of what are merely outliers of lineages evolved on other continents.

The genera are as follows.

There is one species of each of the genera

• Euphorbia (https://en.wikipedia.org/wiki/Euphorbia),
• Sarcostemma (https://en.wikipedia.org/wiki/Sarcostemma),
• Lycium (https://en.wikipedia.org/wiki/Lycium),
• Hoya (https://en.wikipedia.org/wiki/Hoya_(plant)), and
• Disphyma (https://en.wikipedia.org/wiki/Disphyma).

There are a few species of each of the genera

• Carpobrotus (https://en.wikipedia.org/wiki/Carpobrotus),
• Zygophyllum (https://en.wikipedia.org/wiki/Zygophyllum), and
• Sarcocornia (https://en.wikipedia.org/wiki/Sarcocornia).

There are many species in each of the genera

• Tecticornia (https://en.wikipedia.org/wiki/Tecticornia), and
• Atriplex (https://en.wikipedia.org/wiki/Atriplex).

The shrub Maireana pyramidata (https://en.wikipedia.org/wiki/Maireana_pyramidata), belonging to an exclusively Australian genus, hardly qualifies as succulent, because its leaves are extremely small. However, it dominates patches of sodic but non-saline soils over a wide area of southern interior Australia. Maireana pyramidata is convergent in foliage form with the confamilial Salsola (Amaranthaceae: Salsoloideae, https://en.wikipedia.org/wiki/Salsola) of Africa and Eurasia.

The only succulent genera that are speciose in Australia tend to be halophytic. These are

• perennial samphires (Amaranthaceae: Salicornioideae) in the genus Tecticornia, and
• perennial saltbushes in the genus Atriplex.

No genus of succulent perennial plants is restricted to Australia, but Tecticornia is particularly differentiated on this continent with 36 species restricted to Australia and just one shared with India and Pakistan.

I define samphires as annual or perennial members of the Amaranthaceae (https://en.wikipedia.org/wiki/Amaranthaceae) with succulent stems rather than succulent leaves, most but not all of which are halophytic.

The extremely halophytic succulent plants in Australia are, in part, merely the counterparts for ecologically similar relatives in saline environments on other continents.

However, what has previously been overlooked is that several species in Australia surpass the adaptive extremes of plants on other continents that combine succulent foliage with woody stems.

The shrub Tecticornia arbuscula (https://www.inaturalist.org/taxa/465836-Tecticornia-arbuscula) reaches 2 m high (https://www.inaturalist.org/observations/100047992 and https://www.inaturalist.org/observations/106301250 and https://www.inaturalist.org/observations/90123220 and https://www.inaturalist.org/observations/117083495 and https://www.inaturalist.org/observations/60372900 and https://www.inaturalist.org/observations/44119604 and https://www.inaturalist.org/observations/38741317). This makes it the tallest samphire on Earth despite the limitations of a saline habitat. It dominates small patches of halophytic vegetation scattered widely from southwestern Australia to New South Wales and Tasmania.

The shrub Tecticornia arborea (https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:167604-1),
also possessing upright woody stems, and is similarly succulent. However, it is ecologically odd in occurring only on non-saline, possibly acidic clay in mulga woodland in semi-arid Western Australia. This is vegetation (https://en.wikipedia.org/wiki/Mulga_(habitat)) dominated by the low tree Acacia aneura (https://www.inaturalist.org/taxa/188884-Acacia-aneura).

Atriplex nummularia (https://www.inaturalist.org/taxa/75711-Atriplex-nummularia) belongs to a worldwide genus of more than 250 species. However, this species grows larger than any congener, reaching up to 3 m high and 10 m wide (check fact, https://en.wikipedia.org/wiki/Atriplex_nummularia and https://www.inaturalist.org/observations/75153886 and https://www.inaturalist.org/observations/36448963).

Thus, what has been overlooked in the past is the following:
Although succulent shrubs are generally poorly represented in Australia relative to other continents, several species with halophytic affinities excel in plant size and the length of woody stems. One samphire among them, namely T. arborea, has also relaxed the general dependence of its genus on saline, alkaline soils.

Posted on June 9, 2022 02:52 AM by milewski