Psoralea dreweae is a small, largely herbaceous
subshrub, without dot-like glands, that regrows from an underground rootstock after a fire destroyed the vegetation and forms large, often mat-like clumps. It's erect, distinctly ridged and scarcely branching, densely leafy stems are up to long. At the base of the stiff,
alternately set leaves are two awl-shaped
stipules of long and wide, with 5-6
veins, hairless except for a rough margin. In contrast to most
Otholobium species, the leaf only consists of one
leaflet. The ancestral clover-like leaf can still be deduced from the fact that the petiole of long is topped by a
petiolule of about long that can be shed separately. It in turn carries the leaflet that can also be shed separately. The first leaflets to appear are more or less circular and smaller than those higher up the stem. These later leaflets are elliptic in shape, long and wide, with a wedge-shaped base, a sharp, elongated, rigid tip, a rough margin, and mostly hairy on the veins. The flowers are combined in compact and rounded
inflorescences of long, which grow individually at the tip of the shoots on a
peduncle of 25–30 mm long, which is about as long as the leaflets, and consist of 4-6 clusters of three flowers, each triplet subtended by a lance-shaped, pointy bract of long and wide. A persistent bract subtends each individual flower. The
calyx has thick, netted veins, is covered on the outside by very short erect white hairs and long black hairs and hairless on the inside. It is merged at the base into a long tube and has five equally long teeth of . The upper four teeth are all lance-shaped and wide, the one subtending the keel is folded like a boat, long and wide. As in most
Faboideae, the corolla is
zygomorph, forms a
specialized structure and consists of 5 free, initially dark pink petals that later fade to white. The upper petal, called the banner or standard, curves backwards, is long and wide, hairless, has a narrow part at its base called the
claw of approximately long and a vaguely delimited white spot that functions as a
nectar guide. It is broadly oval in shape, without appendages but with prominent
auricles. The side petals, called wings, are longer than keel at long and approximately wide, spade-shaped, curving up, with an auricle, and a long claw at the base, and is sculptured with 50-60 ridges midlength above the middle. The 2 lower petals that stick together at the underside and are jointly called the keel, consist of approximately long claws at the base and about long and wide blades that have a rounded tip. The keel envelops a hollow, open tube of about long, made up of 9 merged
filaments and 1 free stamen, which are topped by 10 equal-shaped anthers of long. Largely hidden in this
androecium is a long
pistil, including the softly hairy ovary of about long at its base, a style that is thickened at the place where it curves upward about 4 mm from its end, hairy in its horizontal part and hairless in the vertical part. The pistil it topped by a pinhead shaped
stigma covered with brush-like hairs. The pistil later develops into the distinctly ribbed, long and thick pod that has a papery texture and a covering of fine, soft, white hairs, and contains just one seed. The seed is about long and long, pale brown in colour with small purple blotches near the area where it was attached.
Differences with related species Psoralea dreweae can be distinguished from
P. thomii that is a semi-erect or decumbent (not erect) plant with initially densely hairy (not sparsely hairy), pliable (not stiff) leaves, that each have at their base 2 softly hairy, broadly oval lance-shaped stipules with a pointy tip (not hairless and awl-shaped), each triplet of flowers is subtended by a lance-shaped bract that is shed quickly (not egg-shaped and persistent), and its petals are light to deep purple in colour (not dark pink that fades to white).
O. lanceolatum and
P. rotundifolia are woody shrublets with cylindrical stems covered with dot-like glands and distantly set leaves (not densely leafy with ridged, herbaceous stems without dots), with pale mauve or white petals (not light to deep purple).
P. zeyheri in which the leaves that are higher on the stems have 3 leaflets (not all leaves with just one leaflet), carries spikes that consist of 25-30 sets of 3 flowers, on a stalk that is 4-5 times longer than the subtending leaf (not 3-9 triplets on an inflorescence stalk just 1-2 times longer). == Taxonomy ==