Phthirusa
Content
Description
Leafy parasites, glabrous or furfuraceous when young; usually epicortical roots from base of plant and, in some, also from branches. Leaves paired, petiolate. Inflorescences not subtended by bracts, basically an indeterminate raceme of sessile or pedunculate triads, each triad with at least median flower sessile, and with bracts and bracteoles which tend to be persistent; in some species, branched (compound) inflorescences in terminal and/or axillary positions. Flowers perfect or plants dioecious, 4- or mostly 6-merous, small, dark red to creamy white; when unisexual, aborted organs of opposite sex present; stamens dimorphic in most species, with basifixed anthers, filaments short and stout, longer ones often with lateral depressions accommodating anthers of shorter ones; style rather massive, with shape of anthers impressed upon it, and thus of uneven thickness. Fruit a berry of diverse colors; seed with copious white endosperm; embryo at maturity bright green, fleshy, dicotylous, with well differentiated haustorial disk. (x = 8, 16).
Distribution
Guianas present, Jamaica present, S America present, Southern America: Bolivia (Bolivia present), north of Costa Rica present, southern Mexico present
Uncertain number of species (see note below); almost exclusively continental, S American genus (2 species on Jamaica), ranging from southern Mexico to Bolivia, only P. pyrifolia being present north of Costa Rica; in the Guianas 11 species.
Notes
The closely related, strictly Caribbean genus Dendropemon (Blume) Rchb. has in the past frequently been synonymized under Phthirusa . The present genus is of uncertain size as it has not been analyzed properly since Eichler's treatment in the Flora Brasiliensis in 1868; it is probably not a natural assemblage. Its separation from Struthanthus is said to be difficult, but this is perhaps due to the lack of attention to the details of floral structure; no Phthirusa species has slender filaments and versatile anthers, as is the case in Struthanthus . Anther morphology in the two genera would seem to be very different, those of Struthanthus being dorsifixed and versatile, those of Phthirusa being basifixed (sometimes sessile), the connective of some species extending into a small horn and the filament massive and laterally excavated (longer stamen series). See also the comments under Struthanthus.