Habit and leaf form. Very peculiar endoparasitic herbs. Plants of very peculiar form; the vegetative parts filamentous, or fungoid. Leaves much reduced (but with 2 whorls of fleshy floral bracts). Plants rootless; totally parasitic. On aerial parts of the host. Perennial. Leaves interpreted as bracts, whorled; fleshy; sessile; simple. Leaf blades (or bracts) oblong to orbicular, or ovate to orbicular. Leaf blade margins entire (or erose). Leaf anatomy. Hairs absent. Extra-floral nectaries absent. Stem anatomy. Secondary thickening absent (the vascular system vestigial or absent).
Reproductive type, pollination. Fertile flowers functionally male and functionally female, or functionally male, or functionally female. Unisexual flowers present. Plants monoecious, or dioecious. Entomophilous.
Inflorescence and flower features. Flowers solitary; sessile; bracteate (reduced leaves, biseriate 8–12 or triseriate 12–15, imbricate, subtend the flowers, crowded, adnate at the base of the ovary, reddish); ebracteolate; malodorous, or odourless; regular; cyclic. Perianth sepaline; 4–6; 1 -whorled; free, or joined; fleshy, or non-fleshy. Calyx (the perianth being the perianth so interpreted) 4–6; 1 -whorled; polysepalous, or gamosepalous; imbricate (usually), or valvate (rarely); regular; blood red (the apex cream), or pink (pale, apex brownish orange); fleshy (often, more or less), or non-fleshy. Sepals oblong, or obovate (or narrowly obovate). Calyx lobes oblong, or obovate. Corolla absent (L). Fertile stamens present, or absent. Androecial members indefinite in number. Androecium 20–100. Androecial members free of the perianth; united with the gynoecium; all equal; free of one another, or coherent; 1–4 -whorled. Androecium exclusively of fertile stamens. Stamens 20–100 (numerous); all more or less similar in shape; with sessile anthers (anthers sessile on column formed from fused stamens and style). Anthers adnate (to column); dehiscing via pores (terminal); unilocular; tetrasporangiate. Pollen shed as single grains. Fertile gynoecium present, or absent (in male flowers). Gynoecium (in female flowers) 4–8 carpelled. The pistil 1 celled. Gynoecium syncarpous (C); synstylovarious, or eu-syncarpous; partly inferior (nearly superior). Ovary unilocular; 1 locular. Gynoecium stylate. Styles 1; apical. Stigmas 1. Placentation parietal. Ovules in the single cavity 20–50; non-arillate; orthotropous, or hemianatropous to anatropous.
Fruit and seed features. Fruit fleshy; indehiscent; a berry; 20–100 seeded (very numerous). Seeds endospermic; minute. Embryo rudimentary at the time of seed release.
Additional comments. Pilostyles collina parasitic on Oxylobium linearifolium, O.atropurpureum and Gastrolobiumm velutinum; P.hamiltonii parasitic on species of Daviesia and Jacksonia.
Etymology. From the Greek for "hat" and "pillar, style".