Alternatively Mitrastemmataceae Makino~ Rafflesiaceae sensu lato in older treatments
Habit and leaf form. Very peculiar endoparasitic herbs. Plants of very peculiar vegetative form; the vegetative parts filamentous, or fungoid. Leaves much reduced (beneath the flower), or absent (if these are regarded as bracts). Plants rootless; totally parasitic (permeating the host tissues, with only the flowers exserted). Parasitic on roots of the host. Leaves alternate, or opposite, or whorled (usually); membranous (scales).
Leaf anatomy. Stomata absent.
Stem anatomy. Secondary thickening absent (the vascular system vestigial or absent). Xylem when present, without vessels. Sieve-tube plastids when present, lacking both protein and starch.
Reproductive type, pollination. Plants hermaphrodite. Pollination entomophilous.
Inflorescence, floral, fruit and seed morphology. Flowers solitary; small to medium-sized; malodorous (often), or odourless; regular; cyclic. Free hypanthium absent.
Perianth sepaline, or petaline, or of ‘tepals’; 4 (?); joined (forming an irregularly undulate or 4-lobed cup); 1 whorled.
Androecium 10–100 (to ‘many’?). Androecial members free of the perianth; coherent (the androecium comprising a domed tube with rings of sessile anthers beneath its apex and a terminal hole, which falls to reveal the gynoecium - cf. Hydnoraceae); several whorled. Stamens 10–100 (to ‘many’?); with sessile anthers. Anthers dehiscing via longitudinal slits; unilocular; tetrasporangiate. Microsporogenesis simultaneous. Pollen shed as single grains. Pollen grains aperturate; 2–3(–4) aperturate; colpate, or porate.
Gynoecium 9–15 carpelled. Carpels increased in number relative to the perianth. The pistil 1 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary 1 locular (with deep intrusion of the placentas). Gynoecium stylate (the style fleshy). Styles 1; apical. Placentation parietal (the placentas deeply intruded). Ovules in the single cavity 50–100 (‘very numerous’, and very minute); non-arillate; hemianatropous to anatropous; unitegmic; tenuinucellate. Embryo-sac development Polygonum-type. Antipodal cells formed; 3; not proliferating; persistent. Synergids pear-shaped. Endosperm formation cellular. Embryogeny caryophyllad, or solanad (?).
Fruit fleshy to non-fleshy; dehiscent to indehiscent; a capsule (tardily dehiscent), or a berry. Capsules when capsular, splitting irregularly. Seeds endospermic; minute. Embryo rudimentary at the time of seed release.
Geography, cytology. Warm temperate to sub-tropical. One species SE asia to W. Malaysia and Japan, the other Mexico and central America. X = 10.
Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Santaliflorae; Santalales. Cronquist’s Subclass Rosidae; Rafflesiales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; Order Ericales.
Species 2. Genera 1; Mitrastemon.