| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Mitrastemonaceae Mak.

Alternatively Mitrastemmataceae Makino; ~ Rafflesiaceae sensu lato in older treatments.

Habit and leaf form. Strange endoparasitic herbs. Plants of very peculiar vegetative form; the vegetative parts filamentous, or fungoid. Leaves beneath the flower, much reduced, or absent (if these foliar organs are regarded as bracts). Plants rootless; parasitic; endoparasitic (exclusivey on Fagaceae, ermeating the host tissues, with only the flowers exserted, often causing 'witches' brooms'); not green; parasitic initially on roots of the host. Leaves alternate, or opposite, or whorled (usually); membranous (scales).

Leaf anatomy. Stomata absent.

Axial (stem, wood) anatomy. Secondary thickening absent (the vascular system vestigial or absent). The axial xylem when present, without vessels.

Reproductive type, pollination. Unisexual flowers absent. 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.

Physiology, phytochemistry. Sieve-tube plastids when present, lacking both protein and starch.

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 III core angiosperms; core eudicot; Superorder Asteranae. APG IV Order Ericales.

Species 2. Genera 1; Mitrastemon.

Illustrations. • Mitrastemon yamamotoi: Engler and Prantl, Nat. Pflanzenfam. 3 (1915).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 8th June 2026. delta-intkey.com’.

Contents