Habit and leaf form. Achlorophyllous herbs. More or less ‘normal’ plants. Leaves much reduced. Plants more or less succulent; totally parasitic. On roots of the host. Annual, or biennial, or perennial; plants with neither basal nor terminal concentrations of leaves. Mesophytic. Leaves small; alternate; spiral; membranous; sessile; non-sheathing; simple. Leaf blades entire. Leaves without stipules. Leaf blade margins entire. Stem anatomy. Nodes unilacunar.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in racemes, or in spikes. The terminal inflorescence unit racemose. Inflorescences terminal. Flowers bracteate (one flower in the axil of each scale); bracteolate (usually), or ebracteolate. Bracteoles when present, adnate to the calyx. Flowers small to medium-sized; very irregular. The floral asymmetry involving the perianth and involving the androecium. Flowers cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk present (fleshy). Perianth with distinct calyx and corolla; 7, or 9–10; 2 -whorled; isomerous, or anisomerous. Calyx 4–5 (fid), or 2 (the four sepals sometimes more or less united into a lateral pair); 1 -whorled; polysepalous (when reduced to 2 members), or gamosepalous; valvate, or open in bud; unequal but not bilabiate; persistent. Corolla 5; 1 -whorled; gamopetalous (the tube often curved); imbricate (the adaxial members internal); bilabiate; yellow and purple; persistent. Androecium 4, or 5. Androecial members adnate (epipetalous); markedly unequal; free of one another; 1 -whorled. Androecium exclusively of fertile stamens, or including staminodes. Staminodes if present, 1. Stamens 4; didynamous; reduced in number relative to the adjacent perianth (the posterior androecial member being absent or staminodal); oppositisepalous; all alternating with the corolla members. Anthers cohering, or separate from one another; dorsifixed; dehiscing via longitudinal slits; introrse; unilocular to bilocular; tetrasporangiate; appendaged (the connective sometimes spurred at the top), or unappendaged. Gynoecium 2 carpelled. The pistil 1 celled. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; synstylovarious, or eu-syncarpous; superior. Ovary unilocular; 1 locular (with 4 placentas). Gynoecium median; stylate. Styles 1; attenuate from the ovary; apical. Stigmas 2 - lobed; dry type; papillate; Group II type. Placentation parietal. Ovules in the single cavity 12–100 (‘many’); non-arillate; anatropous.
Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal, or valvular. Fruit 12–100 seeded (‘many’, with over 100,000 from a plant of O. minor). Seeds endospermic. Endosperm oily. Seeds minute; with starch. Embryo rudimentary at the time of seed release. Seedling. Germination cryptocotylar.
Special features. The upper (posterior, adaxial) lip of the corolla entire, or bilobed; upper (adaxial) lip of the corolla equal to or shorter than the lower lip. Lower (abaxial) lip of the corolla 3 lobed.
Geography, cytology, number of species. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Queensland, New South Wales, Victoria, Australian Capital Territory, and Tasmania. Eremaean Botanical Province and South-West Botanical Province.