Psoralea patens Lindl.

P. eriantha sensu auct., non Benth.; P. discolor Domin.

Woolly-flowered scurf pea, bullamon lucerne (Australia).

A prostrate, rarely erect, soft-wooded, perennial, shrubby legume. Stems several to many, radiating from a central taproot, usually densely clothed with softly spreading hairs. Leaves trifoliate. Leaflets basically ovate, the margins denticulate, glabrous or hoary above, usually more pubescent below. Terminal leaflet 2 to 3 (1 to 4) cm long x 1 to 1.5 (0.7 to 2) cm wide.
Inflorescence an axillary raceme of almost sessile flowers, in groups (usually of three), continuously and usually compactly arranged along the 2- to 3 (1- to 9-) cm-long rachis. Peduncle 2 to 7 (sometimes 1 to 14) cm long. Flowers small, 6 to 7 cm, sometimes to 8 mm long. Corolla pink, purplish or bluish, slightly longer than the calyx. Calyx densely pubescent, hairs white or pale, always dense, the lowest lobe longer than the others and as long as the corolla. Pods more or less enclosed in the calyx, silky-pilose (Lee, 1980).

The typical form occurs in all Australian states except Tasmania. An atypical form, with more or less densely tomentose leaflets, occurs in a broad band from the central Northern Territory south-east across the Simpson Desert to western New South Wales. This species is usually found only on sandy soils, but often on sites with favourable moisture relations (Lee, 1980).

A summer-growing perennial; also gives some winter green growth (even though the tips of the leaves may be damaged by frost). Growth rhythm appears to be more closely related to temperature than rainfall. It is found mainly at altitudes of 300 to 600 m in rainfall regimes of 450 to 750 mm. It is very drought-tolerant and has a deep root system (Figure 3, Chapter 2). Skerman (1957) found that the taproot was still 1.25 cm thick at a depth of 1.5 m and that the roots reach a depth of up to 5 m in deep sandy soils. It occurs most abundantly on sandy levee soils of medium phosphate level (90 ppm available P2O5) and also on heavy clays. De Lacy and Britten (1970) found that it required a soil pH of a least 6.5. The plant is highly specific in its Rhizobium requirements, and two strains, CB762 and CB362, have been isolated from plants in Queensland, Australia, the former being more effective. There is up to 84 percent of hard seed. Dormancy can be broken by scarification or by treatment with sulphuric acid (Kerridge and Skermans 1968).
P. patens grows quite well in association with native Aristida and Heteropogon species of grasses. Slashing of the taller grasses improves its growth and weakens that of the grasses. When established, it successfully competes with local weeds and can smother them with its foliage. The plant is particularly tolerant of defoliation and will regenerate even if the taproot of an established plant is cut 15 cm below ground level on sandy levee soil. Kerridge and Skerman (1968) found that plants survived and grew well even if cut to ground level every six weeks, but performance was better if the plants were cut at the second node at the longer cutting interval of 12 weeks. The additional foliage also improved frost tolerance in winter. It is tolerant of fire, with new shoots quickly arising from the crown.
The plant is very palatable to both cattle and sheep (and also to rabbits), and seed-eating birds harvest a lot of seed. Analyses of the air-dried whole plant revealed 9.6 percent moisture, 15.4 percent crude protein, 3.8 percent fat, 27.6 percent crude fibre, 35.6 percent nitrogen-free extract, 8.0 percent ash, 1.3 percent CaO and 0.41 percent P2O5 (Skerman, 1957). In pot tests, Kerridge and Skerman (1968) found that plants cut at the second node at 12-week intervals yielded as much dry matter as lucerne (alfalfa) cut every six weeks at a height of 2.5 cm.
Flowering occurs in western Queensland (lat. 26°25'S) over an extended period from late September to May. Ripe seed is shed under the plant and is difficult to retrieve except by suction. Its deep-rooting habit, ability to regenerate from a severed taproot, persistence under severe defoliation and maintenance of green leaf after frosting make this plant valuable for the semiarid regions of the Australian tropics. De Lacy and Britten (1970) are endeavouring to breed superior types with a more erect growth habit to facilitate seed collection.
Subsequent work at the University of Queensland has suggested highest annual yields are obtained at longest intervals between harvests, especially from the more erect forms (Gutteridge and Whiteman, 1975; Britten and de Lacy, 1979). Frequent defoliation also markedly reduced the number of primary and secondary shoots, suggesting that survival under grazing may be a more important selection criteria than high yielding ability (Gutteridge and Whiteman, 1975). Yields in the field over the first six months after planting were equal to those of lucerne and higher than those of siratro (Britten and de Lacy, 1979).

This is the plant usually referred to as P. eriantha Benth. prior to the recent clarification of the taxonomy of the P. patens complex by Lee (1980). It is the plant generally referred to by Skerman (1957), de Lacy and Britten (1970), Kerridge and Skerman (1968) and other University of Queensland Department of Agriculture workers. The chromosome number is 2n = 20.

Lee (1980); Skerman (1957).