GYNOECIUM
Pistils of P. subg. Philodendron are closely aggregated on the spadix in a series of irregular spirals. Gynoecial characters have long been considered important in the subgeneric classification of Philodendron and lobed stigmas were used as early as 1832 by Schott in the recognition of his grex Meconostigma and Sphincterostigma (now a synonym of the former). The number of ovules per locule was used by Engler (1878) in part to characterize the two largest sections of the genus, sections Oligospermum and Polyspermium (now Calostigma and Philodendron respectively) (Mayo, 1990).Pistillate flowers consist of a single naked gynoecium lacking staminodia. Typically pistils are ovoid to obovoid or elliptic, and terete in cross-section or with the sides often somewhat irregularly angular by compression owing to their close proximity with adjacent pistils. Each pistil is syncarpous, superior and contains 2-47 carpels (4-10 in P. subg. Philodendron of Central America). They range in size from 0.5 mm (as in P. sousae to 9.2 mm long as in P. advena). The locules are typically oblong with thin translucent walls which extend 2/3 to 3/4 the length of the ovary. Embryo sac development is of the Polygonum-type (Grayum, 1991). The style is barely distinguishable from the remainder of the ovary, distinguishable mostly by being slightly thicker and solid, not translucent. While Dahlgren & Clifford (Dahlgren et al., 1985) deny the presence of a style for Araceae, both Eyde et al. (1967) and Mayo (1986, 1989) indicate that the region has a distinct anatomy. Mayo (1989) defines the style of Philodendron as "that portion of the gynoecium between the base of the stigmatic epidermis and the ovary locules." Typically the style is not obvious, appearing as simply a thickened portion of the pistil apex. Slender, conspicuous styles are rare in Philodendron but do exist as in P. jacquinii in P. sect. Macrogynium (Fig. 242).
Each carpel is connected to the stigma apex or compitum (common stylar canal which may lead to the stylar canals) by a stylar canal. The compitum (Endress, 1982) is a cavity or complexly shaped channel into which the pollen may be inadvertently packed by the beetle pollinators. This no doubt allows that enough grains are left to insure pollination and not later removed from the stigma by movements of the beetles. Stigmatic epidermis extends into the compitum from the stigma apex (Mayo, 1989). At the base of the channel or cavity there is a ring of holes which lead into the stylar canals. Where no compitum is present, such as with "Type B" and "Type D" styles (see section on Style Types below) the stylar canals lead directly onto the surface of the style. These stylar canals are readily visible on the dried stigmas of many species if the preservation is adequate. They are particularly easy to see in fruiting collections.
The gynoecium has a separate stylar canal for each carpel (see Fig. 1 in Mayo, 1989) each of which may open at its upper end into a compitum. The presence of a compitum is rare among Central American species (see section on Style Types below) but is present in P. correae, P. ligulatum var. heraclioanum, P. smithii, P. straminicaule, and P. warszewiczii. A compitum has also been seen on an unusual collection of P. radiatum and some populations of P. tripartitum.
The vascular anatomy of the ovule has been studied by French (1986). Of the five species he studied, three were South American, namely P. acutatum, P. solimoesense, and P. venosum, while two species, P. jacquinii (as P. hederaceum) and P. immixtum, occur in Central America. French reported a single vascular trace for all of these except P. jacquinii (as P. hederaceum) which has multiple traces. Carvell (1989) reported that the vasculature of the gynoecium arises from a single trace which divides centrifugally to yield a single branch trace for each locule. The carpel traces branch once to form a connection with the placenta as well as a single dorsal trace. The placental trace forms individual connection with each ovule (Carvell, loc. cit.).
Finally a few miscellaneous anatomical features of the gynoecium should be mentioned. Both tanniniferous idioblasts as well as raphide idioblasts are lacking in the gynoecium of Philodendron but the gynoecium does contain druse idioblasts (Carvell, loc. cit.). Like most Araceae, Philodendron has unicellular ovular and placental trichomes (French, 1987). These function in secreting mucilage presumably for the protection of ovules.
Ovules of Philodendron are bitegmic, with the inner integument forming the micropyle. The integuments are usually completely free from one another (Grayum, 1991).
