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The families of flowering plants

L. Watson and M.J. Dallwitz

Rafflesiaceae Dum.

Including Patmaceae Schultz-Schultzenst., Pistiaceae C.A. Agardh (p.p.); excluding Apodanthaceae Van Tiegh., Cytinaceae Brongn., Mitrastemonaceae Mak.

Habit and leaf form. Very peculiar endoparasitic herbs. Plants of very peculiar vegetative form; the vegetative parts filamentous, or fungoid. Leaves absent (disregarding the numerous, imbricate floral bracts adnate to the base of the ovary of the large, sessile flowers). Plants rootless; totally parasitic (on Vitaceae, permeating the host tissues, with only the flowers exserted). Parasitic on roots of the host (and rhizomes).

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

Reproductive type, pollination. Plants monoecious, or dioecious (?). Female flowers with staminodes. Pollination entomophilous (the large flowers foetid).

Inflorescence, floral, fruit and seed morphology. Flowers solitary; (multi-) bracteate (the numerous, imbricate bracts adnate to the inferior ovary of the sessile flower); large to very large (including Rafflesia arnoldii with the largest known flowers, these being up to 1 m in diameter); malodorous; regular; cyclic. Floral receptacle developing an androphore (male flowers), or developing a gynophore (female flowers), or with neither androphore nor gynophore (depending on interpretation of the floral columns). Free hypanthium absent.

Perianth ambiguously sepaline, or petaline, or of ‘tepals’ (but distinct from the bracts); 5 (Rafflesia), or 10 (Sapria); free, or joined (?); 1 whorled (Rafflesia), or 2 whorled (Sapria); sepaloid, or petaloid (?); spotted (at least sometimes), or without spots (?); fleshy, or non-fleshy (imbricate).

Androecium of male flowers 5–100 (to ‘many’). Androecial members free of the perianth; united with the gynoecium (or at least, with the stylar column); free of one another (in 1–several cycles beneath the expanded apex of the stylar column); 1–4 whorled (? - to ‘several’). Androecium exclusively of fertile stamens. Stamens 5–100 (to ‘many’); with sessile anthers. Anthers dehiscing via longitudinal slits, or dehiscing via pores, or dehiscing transversely (?); extrorse; bilocular; tetrasporangiate. Microsporogenesis simultaneous. Pollen shed as single grains. Pollen grains nonaperturate; 2-celled (in Rafflesia).

Gynoecium (in female flowers) 4–8 carpelled (?). The pistil 1 celled, or 4–8 celled (via deeply intruded placentas). Gynoecium syncarpous; synstylovarious, or eu-syncarpous (the stout, columnar style in Rafflesia expanded into a large disk, with numerous stigmatal projections on top, the columnar disc of Sapria with a single one); inferior. Ovary 1 locular, or 3–10 locular (by deep intrusion of the placentas). Styles 1; apical. Placentation when unilocular, parietal (the placentas variously intruded or branched); when plurilocular, parietal (or with the very minute ovules covering the inner surfaces of the partitions). Ovules in the single cavity 50–100 (‘very numerous’, and very minute); 25–100 per locule (‘very numerous’); non-arillate; hemianatropous to anatropous; bitegmic (with rudimentary outer integuments); tenuinucellate. Outer integument not contributing to the micropyle. Embryo-sac development Polygonum-type. Antipodal cells formed; 3; not proliferating; persistent. Synergids pear-shaped. Endosperm formation nuclear. Embryogeny caryophyllad, or solanad (?).

Fruit fleshy, or non-fleshy (?); dehiscent, or indehiscent (?); a capsule, or a berry (?). Capsules (if 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. Paleotropical. Sub-tropical to tropical. W. Malaysia , and (Sapria) Assam to SE Asia. X = 12.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Santaliflorae; Santalales (cf. Hydnoraceae). Cronquist’s Subclass Rosidae; Rafflesiales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Malpighiales.

Species about 20. Genera 3; Rafflesia, Rhizanthes, Sapria.

Illustrations. • Technical details: Rafflesia. • Technical details: Rafflesia, Cytinus (Cytinaceae).

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: 30th September 2017.’.