Australian Floral Emblems -
Gossypium sturtianum

The genus Gossypium is noteworthy for its several species that produce the cottons of world commerce. Cotton agriculture and the spinning weaving industries that are based upon it have had a profound influence on the course of human history and have, indeed, changed its direction markedly at certain times. The origins of these cultivated plants are to a large extent lost in the mists of antiquity, but intensive study by many scientists has enabled us to infer much about them. Less well-known, perhaps, are the wild relatives of these cultigens, the 40 or so species of Gossypium that occur as perennial shrubs in the desert areas of Mexico, Africa and Australia. The least well-known of these are doubtless the plants that are native to Australia.

Gossypium typically has showy malvaceous (Hibiscus-like) flowers that last but one or two days. The corollas of most of the Australian species are mauve with a dark spot in the centre. This colour is not found in the genus outside of Australia. Each flower is subtended by an involucel or epicalyx that is uniformly composed of 3 floral bracts, a feature that most clearly sets off Gossypium from its nearest Australian relatives, including Thespesia, Hibiscus and Alyogyne, all of which have involucels of more than three bracts.

Another characteristic feature of Gossypium (which it shares with Thespesia) is the presence of small, dark glands in most parts of the plant. These are obscured in some cases (eg. G.australe) by overlying hairiness but can readily be demonstrated by careful observation. They are quite prominent in certain other cases (eg. G.sturtianum) but are lacking entirely in Alyogyne and Hibiscus. These glands contain the substance gossypol, an undesirable constituent of the edible oil extracted from cotton seed which is toxic to non-ruminant animals.

The leaves of Gossypium typically have one or more nectaries on the under-surface of the leaf, on the midrib and principal veins. Similar structures (three in number) are found at the base of the involucre of each flower. They may be small and obscure or quite prominent, depending on the species.

In addition to the native Australian species of Gossypium, a sizeable cotton crop is grown in various parts of Australia. Of note also are the little-known cottons that are found along the river banks in parts of Arnhem Land, apparently established as a part of the natural vegetation. These are plants representative of the cultivated species, G.hirsutum (which derives ultimately from Middle America), but how or when or by what agent these plants arrived in northern Australia is not clear. They bear handsome white cotton.

Some of the Australian gossypiums have been assigned to various other genera at certain times, most commonly to Cienfuegosia and Notoxylinon. Cienfuegosia is a genus of perennial herbs and sub-shrubs that occurs in Africa, South America, and the Caribbean, reaching the very southern fringes of North America. It does not occur in Australia. Notoxylinon was established as a separate genus to include most of the Australian cottons but it is now considered that there is no basis for the generic distinction.

None of the species has a generally accepted vernacular name, except Gossypium sturtianum, Sturt's Desert Rose. The name "Desert Rose" has also been applied to G.australe.

It is a desert plant and can tolerate drought. However, it responds well to an adequate water supply. Like all species of Gossypium, it thrives on full sun and high temperatures. Even slight shading will inhibit flowering. It is the most cold tolerant of the species and will remain evergreen if not subjected to severe frosts.

Sturt's Desert Rose is rather widely distributed in the interior of Australia. It occurs in the southern part of the Northern Territory, in the north-eastern parts of South Australia, and through much of the western parts of Queensland and New South Wales.

Gossypium sturtianum var.nandewarense differs from the more common form in the much more open growth habit of the shrub and the lighter green foliage. Its flowers are larger but considerably less abundant. It is more cold tolerant than the common form and will withstand light to moderate frosts. The plant derives its name from the Nandewar range near Narrabri in north-eastern New South Wales. It is also known from another limited area in the vicinity of the Expedition Range in eastern Queensland.

This article is based in part on "Desert Roses" by Paul A Fryxell, which appeared in the June 1966 issue of the Society's Journal "Australian Plants". Some amendments have been incorporated to update some of the data.

Notes on botanical terms:

• Corolla - the petals, collectively
• Epicalyx - an arrangement of bracts at the base of the calyx and seemingly forming a second calyx
• Involucre - a cluster of overlapping bracts surrounding the base of the flower head
• Nectary - a specialised gland which contains nectar

Australian Plants online - June 1997
The Society for Growing Australian Plants