16 
Nancy T. Btjriuihh: 
they become old, coarse and unpalatable is used throughout the area. This 
means that there are odd patches in all paddocks, where a certain amount of 
herbage is available to the grazing animal. As a general rule this is entirely 
eaten out by the sheep before they will touch the rough fare offered by the 
tussock grasses. Top feed is not important in the spinifex areas. 
The majority of the rest of the species come under the heading of Buck 
Spinifex, i.e., very rigiddeaved forms in comparison with T. pungens which 
is commonly called “ Soft Spinifex.” The value of Buck spinifexes to the 
pastoralist is very small. In most cases the seedheads are eaten by stock. 
Some species regenerate less readily than others. As a whole the spinifex 
association is an extremely stable one, ecologically. This is a fact of prime 
importance when the risks of soil erosion as a result of denudation by grazing 
animals is considered. So far the spinifex plains do not seem to be showing 
any marked deterioration but along the rivers which serve as stock routes 
there has been serious depletion as a result of overgrazing or of floods follow- 
ing heavy stocking. However in such habitats the Triodia association gives 
way to a savannah type with Eucalypts and annual grasses. 
T. pungens is the only resinous species among these discussed in this 
paper. The gum is used by natives for many purposes, e.g., for fastening 
axe or spear heads to their shafts. So highly is it valued by the uncivilised 
tribes that it is an important item in bartering and even serves as a form of 
currency. It is believed that the seeds of a number of species are eaten. 
History and Limitation of the Genus, 
Triodia was described by Robert Brown in Prodromus Florae Novae 
Hollandiae p. 182 : 1810. The name refers to the triclentate character of the 
lemmas. Bentham (Benth. et Hook. F. Gen. PI. iii. 1175, 1883) and Hackel 
(Engl. u. Prantl., Nat. Pflanzenf. IIAbt. 2. 68) took a wide view of the genus 
and included certain North American species. However, Stapf in his arrange- 
ment of the material in the Kew Herbarium (Hubbard in Hook. leones PI. 
Vol. iv. t. 3336, 1937) restricted the name of the Australian species and placed 
most of the American material in Tridens. This is a much more satisfactory 
arrangement. The lemmas in the American material are definitely three 
nerved and the outer nerves are more or less marginal. In the Australian 
species the nerves are in three groups of three or more, each group ending in the 
lobes and where the group is reduced to a single nerve it is not uncommon to 
find vestiges of nerves at the base. There is also a tremendous difference in 
the general habit of the two sets of species. While the American species are 
small tufted grasses the Australian ones are large tussocks with rigid, pungent 
pointed leaves. The odd geographic range must also be considered. There 
is a general resemblance between the habitats the two genera occupy. 
Brown described four species of which T. pungens is the type for the genus. 
None of the type material was collected in Western Australia. Bentham (FL 
Austral, vii. p. 605 : 1878) however, had the use of a larger amount of material 
and he listed T. pungens and T. microstarhya for this State as well as his own 
species T. Cunninghatnii. Concerning the first of these Hubbard (Hook. 
Ie. II. \ ol. iv. , t. 3336, 1937 ) has declared that the western material represents 
a distinct species. Nevertheless the author, as a result of field work, is con- 
vinced that the variations existing bridge the gap of the eastern material and 
definition, even as a variety, is not possible. Lhis decision is supported bv 
the agreement in foliar anatomy. T. microstarhya is reported for the North- 
West Coast owing to a speciman collected by Cunningham. This specimen 
was seen, by the author, while at the Kew Herbarium in 1 940 and it represents 
