Ptychosema pusillum, more commonly known as Dwarf Pea, is listed as Vulnerable under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and under the Wildlife Conservation Act 1950.
The main threats to Dwarf Pea include grazing; weeds; inappropriate fire regimes; changes in hydrology; firebreak and power line maintenance; and dieback caused by Phytophthora cinnamomi. This species should be protected from fire until its fire response is better understood.
Ptychosema pusillum is the only Western Australian representative of its genus. It is an erect herb-like plant, growing to 10 cm tall. Its pinnate leaves are divided into 5–11 narrow, oval leaflets, each of which is 2–10 mm long and 1–2 mm wide.
Single pea-shaped flowers are borne on leafless stalks, about 6 cm long, from August to November. The large, 1.5 cm long, standard petal is orange, striped with deep red on the upper side, with a yellow ‘eye’ at the base. The back of this petal is dark brown, with yellow stripes.
The other petals are dark red. The fruit is a flat, dry pod which splits down both sides to release a few hard seeds. The flower resembles that of Lamb Poison (Isotropis cuneifolia), but Dwarf Pea differs in its divided leaves
Dwarf Pea is endemic to Western Australia and is known from three populations, all of which are located on private property. Two populations are located near Gingin, with another further north, near Reagans Ford.
The species is estimated to have several thousand mature plants; however, precise figures are unavailable as full surveys have not been conducted in recent years. The extent of occurrence is estimated to be 280 km2.
Dwarf Pea inhabits low, open woodland of Slender Banksia (Banksia attenuata), Firewood Banksia (B. menziesii) and Eucalyptus todtiana over scrub with Common Woollybush (Adenanthos cygnorum) and Yellow Buttercups (Hibbertia hypericoides). In the north, it occurs on the upper slopes of a high sand ridge. Near Gingin, one population occurs adjacent to a paperbark swamp and the other is found throughout open vegetation and firebreaks.
Information Source: Government of Australia, Department of Environment and Department of Parks and Wildlife Western Australia