Sunday, May 2, 2010

Lawrencia helmsii

Lawrencia helmsii (Malvaceae): Dunna dunna.

If you are travelling through the midwest regions of Western Australia, you may chance upon this chunky, straggely, cactus-like shrub that's about 1 - 1.5 m tall and just as wide.

Lawrencia helmsiiLawrencia helmsii  - Dunna Dunna

It isn't a cactus, despite appearances, and we don't have Cactaceae native to Australia. But, it is a member of the mallow or hibiscus family (Malvaceae) and is a hardy occupant of dry, rocky gypsum and calcrete soils in the midwest regions of Western Australia. These tend to be mineral-enriched, clayey, saline, basic soils (pH abouts 8.0 ), often on or around rocky rises and saline / gypsum flats. This one we encountered was c. 70 km - 100 south of Newman, but we failed to take notice of exactly where we were along a seemingly endless stretch of the Great Northern Highway. No doubt however  - we were at the extreme northern limit of its distribution.

Despite initial appearances as a chunky monstrosity, Lawrencia helmsii - the Dunna Dunna, is a intricate plant when explored up close. If you look carefully at one of the many hundreds of tiny flowers which crowd along on the stems, you see that it is close to a mallow or hibiscus flower. Well - you are hard-pressed to see much really, and you need a bit of imagination. And these flowers are about -- oh - about 5 mm in diameter. This is a flower from a male plant which I have photographed - the species is actually dieocious. There is not much to these male flowers - five tiny reddish-green petals, a staminal column with a cluster of anthers at the top. The female flowers are similar, but with more style and less dangly bits.


These flowers are emerging directly from the woody stem on a very, very short stalk (they're close to sessile, really), between the tightly packed, very short branches crowded with tight clusters of scaley leaves. Looking at the stems in detail is like a trip into an ever-shrinking world of tiny, fine features.  There are about 14 species/taxa of Lawrencia in Western Australia (which is the sum total of the species in Australia), and a couple of these are equally as bizarre as L. helmsii (like L. chrysoderma). I have included informally named taxa in that count.

Lawrencia helmsii has been described as a succulent, but that's only really because the tiny, tiny leaves are sort-of succulent. I'm not convinced. The stem is certainly not - it is woody and tough and sort of spongy like balsa wood. These main stems are certainly not a source of juice or water for the thirsty in the desert.

Because these are such weird-looking plants, there is some interest in growing them as an ornamental - but they grow in such a relatively extreme habitat that I'm not sure how they would go in an ordinary garden - unless you lived on a gypsum flat.

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