OVARY LOCULE NUMBER
Mayo (1991) reports ovules in P. subg. Meconostigma range from 3-47 locular and Bunting (1986) reports two (rarely three) locules per ovary as being characteristic of P. sect. Philopsammos.
Though the number of ovaries per locule is highly significant in separating P. sect. Philodendron and P. sect. Calostigma, the number of locules per ovary is not a good indicator of relationship. For example P. sect. Calostigma has an average of 5.5 locules per ovary for the minimum and an average of 7.4 locules per ovary for the maximum locules per ovary while comparable figures for P. sect. Philodendron is 4.6 for the average minimum and 6.1 locules per ovary for the average maximum. While the average number of locules per ovary has a slightly lower range for P. sect. Philodendron (4.6-6.1 versus 5.5-7.4 for P. sect. Calostigma) the difference appears to be insignificant. In P. sect. Calostigma the number of locules per ovary ranges from 1 per ovary to 10 per ovary. In P. sect. Philodendron they range from 3-10 locules per ovary. There are small, though insignificant differences in the average range of locules per ovary for the two sections. While the genus as a whole in Central America generaly has 4-8-locules per ovary, P. sect. Philodendron most commonly has 4-6 loculed ovaries and P. sect. Calostigma most commonly has 5-8 loculed ovaries. Moreover, while P. sect. Philodendron rarely has locules more numerous than eight per locule, P. sect. Calostigma rarely has fewer than five locules per ovary, while more species (14 in all) have eight locules per ovary than any other number.
Though 4-celled locules are fairly common in P. subg. Philodendron, with 33 Central American taxa having at least some 4-locular ovaries, and with all but seven of these representing the lowest number of locules per ovary for the species represented. Four species, P. cretosum, P. jacquinii, P. knappiae, and P. subincisum, so far have demonstrated only 4-locular ovaries. Most species, eight in all, with 4-locular ovaries also have 5-locular ovaries on the same spadix. One species, P. squamicaule has 4-5 locular ovaries but also may have 3-locular ovaries. Six species have 4-6 locular ovaries. Two species have 4-7 locular ovaries, three species have 4-8 locular ovaries and one species each have 4-9 locular ovaries and 4-10 locular ovaries
Five locules per ovary is the minimum number in 29 species while for 15 species 5 is the maximum number of locules. A total of four species showed exclusively 5-locular ovaries. Six locules is the minimum number for 11 species and the maximum number of locules per ovary for 23 species. Seven locules per ovary is the minimum for eleven species and the maximum for 13 species. Only four species have a minimum of eight or nine locules per ovary but 24 species have these numbers for the maximum number of locules. Only eight species have locule numbers greater than ten. All but one of these are in P. sect. Calostigma.
Three-locular ovaries are rare and only two species, P. copense and P. sagittifolium, regularly have 3-locular ovaries. Several other species, including P. chirripoense, P. hederaceum, P. immixtum, P. morii, and P. squamicaule may rarely have 3-locular ovaries. No species of subg. Philodendron in Central America was found with bilocular ovaries though two species, P. sagittifolium and P. zhuanum were found with only a single locule. In the case of the latter species the number of locules ranged only from 1-3 but in P. sagittifolium the number of locules ranged up to eight. Often such odd low locule numbers occur only near the base of the spadix where the ovaries are often somewhat irregular in shape. Often the lowermost pistils on the spadix are larger or smaller than those in the middle of the spadix and they are frequently more widely spaced and of irregular cross-sectional shape.