Rafflesiaceae s. str.

Genera Included:Rafflesia, Rhizanthes, Sapria. This circumscription agrees with the arrangement of Harms (1935) and Bouman and Meijer (1994) that segregated these genera into tribe Rafflesieae. Similarly, Takhtajan (1987) split Rafflesiaceae s. lat. into Apodanthaceae, Cytinaceae, Mitrastemonaceae and Rafflesiaceae s. s. Molecular evidence (nuclear SSU rDNA and mitochondrial genes) supports a close relationship between Rafflesia, Rhizanthes, and Sapria.

Habit: Achlorophyllous, holoparasitic herbs; often with abundant tannins.

Parasitism: Stem and root parasites.

Roots: the endophyte filamentous or plate-like, resembling a fungal mycelium inside the host tissues.

Stem: Absent

Leaves: Absent or at most reduced to bracts present around the base of the flower.

Inflorescence: Flowering shoots formed endogenously within the host; flowers single, arising from a basal cupule.

Plant Sex: Plants monoecious or dioecious; flowers generally unisexual. Rhizanthes has bisexual, male and female flowers.

Flowers: Actinomorphic, from 8 cm (Rhizanthes) to over a meter (Rafflesia). The flowers of Rhizanthes range from pure white to brown. Rafflesia is orange, brick red with white spots, or even yellow and black, often malodorous (decaying protein). Usually subtended by varying numbers of floral bracts.
Calyx (perianth): Perigone lobes 5 in Rafflesia , 10 in Sapria, and up to 16 in Rhizanthes; connate below, imbricate (or valvate in Rhizanthes). In all three genera, the perianth is fused distal to the ovary into a perigone tube. The tips of the perigone lobes of Rhizanthes have long, vermiform appendages. In Sapria and Rafflesia (but not Rhizanthes), the perigone tube produces a centrally located aperture called the diaphragm. The interior of the floral chamber of Rafflesia and Sapria contains unusual, often branched or clavate trichomes ("ramentae") that have taxonomic use. At the base of the perigone tube are two concave regions known as the inner and outer annuli.
Nectary: The ramenta inside the flower tubes of Rafflesia, Sapria, may function as nectaries or osmophores.
Androecium: The androecium of Rafflesia occurs on the underside of the collar of the central disk. The 5-many anthers originate in one series in most members. In Rhizanthes, the anthers form a ring around the lower margin of the column disk and number ca. 38-50, each with 2 superimosed loculi. Dehisce is through two pores whereas in Rafflesia the anther is multiloculate and dehisces through one pore.
Disk: The column is expanded above the anthers (e.g. in Rafflesia) to form a disk bearing numerous horn-like processes. The stigma is found in a similar position in female flowers. The disk of Sapria is peltate but lacks processes.
Pollen: The sticky/slimy pollen of Rafflesia is dehisced en mass. Binucleate, multiaperturate to 2-3 porate or inaperturate, not sculptured. All three genera have unisulcate ulcerate pollen with a lamellate endexine and an additional perinium-like supraexinous layer.
Gynoecium: Epigynous. Carpels 4-8, syncarpous, 1-locular (Rhizanthes) to a a multilocular network (Rafflesia) by numerous, irrregular intrusive placentae that form a maze-like configuration in cross section. Columnar style expanded at apex into a disk. Male flowers in Rhizanthes have a rudimentary ovary.
Ovule: Numerous, covering the surfaces of the placental partitions. Anatropous to orthotropous, unitegmic, tenuinucellar (see Bouman and Meijer 1994).
Embryo:

Pollination: Flies (for Rafflesia, see Beaman et al., 1988, Amer. J. Bot. 75:1148; for Rhizanthes see Bänziger 1995, 1996).

Fruit: Indehiscent or irregularly dehiscent fleshy berry, with numerous small seeds. Rafflesia requires 6 -8 months for the blackish-brown fruit to mature.

Fruit/Seed Dispersal: Fruits of Rafflesia are eaten by squirrels (Callosciurus) and tree shrews (Tupaia) which implicates them as the seed dispersers (Nais 1992). A wider range of epizoochorous dispersers have been suggested (elephants, wild pigs, tapirs), but rodents, anteaters and pangolins are more plausible. Seed dispersal in Rhizanthes and Sapria has not been documented.

Seed: Peanut-shaped, i.e. composed of two unequal parts: distal with embryo and endosperm, proximal part composed of the rudimentary outer integument, chalaza, raphe and part of the funiculus. Hard schlerenchymatous outer testa.

Embryology:

Embryo Sac Development: Polygonum type (Cocucci 1983, Olah 1960).
Embryo: tiny, undifferentiated, composed of few cells, no suspensor.
Endosperm one-layered, composed of 30 -40 cells, oily.

Chromosomes: Rafflesia (n=12), Rhizanthes (n=11).

Link to Family Description in Delta


SIUC / College of Science / Parasitic Plant Connection / Rafflesiaceae / Description
URL: http://www.parasiticplants.siu.edu/Rafflesiaceae/description.html
Last updated: 15-May-06 / dln