Perusing the peas of SA

Date posted: 24 May 2016

GALLERY: See stunning Swainson-peas by clicking the gallery on the right (all images courtesy the Seeds of South Australia website)

Most of us are familiar with South Australia’s floral emblem, the iconic red-and-black Sturt’s Desert Pea (Swainsona formosa). The plant is well-known from many arid parts of Australia, excluding Victoria and Tasmania. But did you know there are a number of other stunning desert peas that only occur in SA? Some of these are extremely rare and unique. Of the 42 species of swainson-peas recorded in our state, nine of these are endemic. And with recent high rainfall around the state, plenty of these striking peas may pop up this spring.

Want to help save SA's threatened peas? See what you can do to help.

Let’s take a look at some of the unique plants you may come across:

• The rare Darling swainson-pea (Swainsona murrayana) is better known from the Darling and upper Murray River catchment, but this disjunct occurrence was only just rediscovered in SA on Boolcoomatta Station near the state’s eastern border. It was last recorded in SA in 1926 by Morris and it grows on chenopod (less than 1.5 metre tall) floodplains on a retired pastoral lease now managed for conservation by Bush Heritage Australia. A spectacular looking (although tough to spell!) swainson-pea found growing with the murryana was Swainsona swainsonioides (aka Downy Darling-pea).
• Some annual swainson-peas only ever appear after mallee bushfires such as Bladder pea (Swainsona colutoides) and the rare Yellow swainson-pea (Swainsona pyrophila). After a bushfire these short-lived fire-responsive peas can appear in many hundreds, but after two-to-three years it will be impossible to locate a single plant.
• Some swainson-peas that occur in the arid rangelands of South Australia won’t be seen for many years, persisting only in the soil seed bank and awaiting good seasonal rains. In the optimum rainfall years these annual swainson-peas can rapidly grow to 1.5 metres tall. Examples of these include Woolly Darling Pea (Swainsona burkitti), which is only known in SA from two localised areas in the Flinders Ranges. In 2010 waist-high fields of this purple pea could be seen into the horizon near Parachilna (just east of Lake Torrens), but not a single plant has been observed in subsequent years of driving down the same highway.
• Grey swainsona (Swainsona canescens) is another large pea that flourishes in good years, growing on red sand plains in their hundreds, especially in the Gawler Ranges and Great Victoria Desert regions.
• Gypsum Swainson-pea (Swainsona unifoliata) is a rare gypsophila (gypsum-loving) species that has been recorded in just a few freshwater soaks in Australia’s largest desert, the Great Victoria Desert (spread across Western Australia and SA). The pea is quite restricted to this niche growing on the soft gypseous outcrops in the immediate surrounds of the well or soak.

Some of the interesting swainson-peas endemic to SA include:

• The Tarcoola pea (Swainsona dictyocarpa) was previously only known from two historic collections, the latter in 1948 from Bitter Well near Kingoonya in SA’s central outback. The collector that year was renowned naturalist J.B. Cleland. This swainson-pea was rediscovered almost 60 years later by the SA Seed Conservation Centre in 2010, and it’s still only known from this single localised population. It wasn’t until this recent discovery that we learnt more about this plant species, such as its habit and flower colour.
• The Dark Green Swainson-pea (Swainsona fuscoviridis), which is a very rare pea mainly restricted to the Barrier Ranges region, which straddles SA and New South Wales.
• The Creeping Darling-pea (Swainsona viridis), which is an iridescent bright green in good seasons and mainly occurs in the Flinders Ranges region.
• Ashy-haired Swainson-pea (Swainsona tephrotricha), which is a rare pea restricted to the Mid North region and the Gammon Ranges (in the North Flinders Ranges).
• The Hairy Swainson-pea (Swainsona vestita), a rare pea historically known from a single locality east of Coober Pedy. A number of populations have since been recorded in the region during field work in 2010. This compact hairy herb has erect (vestite) hairs and pea flowers that can be purple or yellow.

Heading to the beautiful Lake Eyre region this year in light of the recent rainfall? Here are some of the attractive swainson-peas you might spot in the South Australian rangelands:

• The Slender Darling-pea (Swainsona tenuis) can be found near Cadney Park, 151 kilometres north of Coober Pedy, on the Stuart highway.
• The Orange Swainson-pea (Swainsona eremaea) was photographed in fields along the Oodnadatta Track in spring 2010 (see gallery on right).
• Yellow Swainson-pea (Swainsona laxa) is a shrub to 1.5 metres tall with yellow flowers that grows in the Lake Eyre region.
• Coast Swainson-pea (Swainsona lessertiifolia) is a predominantly coastal swainson-pea species that has disjunct populations that occur as far inland as Tarcoola in the state’s far north.

So there you have it – while the iconic Sturt’s Desert Pea is still a favourite, now you know some of the other utterly beautiful Swainson-pea gems we can call our own!