P. aciculatum is a geophyte with erect leaves and rigid petioles. The laminae are irregularly deeply pinnatilobed to pinnatisect and densely hirsute with appressed hairs. The hypanthia of the small yellow flowers are about twice the length of the calyx. There are five fertile stamens, of which the posterior one and the lateral two are very short and concealed within the floral sheath. The lateral two are recurved so that the anthers are borne on the same level as that of the posterior one. The anterior two stamens are about the same length as the calyx and protrude from the flower. The petals are about 1.5 times the length of the calyx, with wine-red feather-like markings on the posterior two. The specific epithet refers to the irregular fine streaks on the petals.
A deciduous geophyte with a subterranean tuber, leaves erect, 100-300 mm high when in flower. Tuber: elongated, branched roots, sometimes with more than one stem-growing point, covered with dark brown periderms, 80-100 mm long and ±20 mm in diameter. Leaves: radical, petiolate, green; lamina elliptic, 100-140 x 35-60(-80) mm, irregularly deeply pinnatilobed to pinnatisect, densely hirsute with distally appressed hairs and glandular hairs interspersed; segments linear, 6-12 mm wide, apices acute, margins serrate; petiole 50-130 mm long, rigid, hirsute with coarse hairs and glandular hairs interspersed; stipules subulate, 18-25 mm long and 2 mm wide, ciliate, adnate to the petiole with apices free; free apices ±8 mm long. Inflorescence: scape 60-130 mm long and 2-3.5 mm in diameter, light green, densely pilose with curly hairs interspersed with long glandular hairs, branched, bearing 2-4 pseudo-umbellets; peduncles 50-130 mm long and 1-1.5 mm in diameter, indumentum as on scape; bracts irregular in form and size, densely hirsute with appressed hairs; pseudo-umbellet 13-32(-40)-flowered, subtended by a whorl of spathulate bracts; bracts 3-5 mm long, acuminate, adaxially hirsute with appressed hairs, abaxially hirsute with appressed hairs and interspersed with glandular hairs, initially erect, recurved during senescence; flower buds, flowers and fruits erect. Pedicel ±1 mm long. Hypanthium 12-16 mm long (about twice as long as the calyx), light green, indumentum as on scape. Sepals 5, 7-9 x 1.5-3 mm, posterior one erect, others recurved, lanceolate, apices acuminate, light green, indumentum abaxially as on scape, only less dense. Petals 5, pale yellow or cream-coloured, claws orientated close together forming a sheath-like structure; posterior two ligulate, 11-13.5 x 2-3.5 mm, curved laterally, with feather-like red markings, bases cuneate, apices rounded to emarginate, laterally recurved during anthesis; anterior three spathulate, 9-10 x 2-2.5 mm, dimly marked pink at the very base, bases narrowly cuneate, apices rounded to emarginate, patent during anthesis. Stamens 10, basally connate, staminal column 1-2 mm long, white; perfect stamens 5, posterior one ±1 mm long, lateral two 2 mm long, recurved so that anthers are home on the same level as posterior one, anterior two 6.5-8 mm long, protruding from the flower, free filaments dark pink; staminodes ±2.5 mm long; anthers 1 mm long, dark pink, opening with longitudinal slits, pollen orange. Gynoecium: ovary superior, oblong-conical, 5-lobed, 4.5 mm long, densely sericeous, green; style filiform, 3-4 mm long, dark pink; stigma with 5 branches, branches 1 mm long, dark pink. Fruit: a schizocarp consisting of 5 mericarps, bases of mericarps ±4 mm long and tails ±23 mm long.