Seeds of P. subg. Philodendron are few to many per berry, and are mostly oblong to oblong-ellipsoid, ellipsoid, ovoid-oblong or less frequently ovoid. Typically they are minute (see below). Seeds are typically more or less terete in cross-section though they may be somewhat flattened, e.g., P. findens They have a rather thick, smooth (e.g., P. granulare) or striate-costate testa as well as copious endosperm. The longitudinally oriented striations may be weak (P. advena, P. findens, P. cotonense, P. purpureoviride and P. sagittifolium) or strong (P. ferrugineum and P. grandipes). Philodendron microstictum has both longitudinal striations and much finer cross-etching. A number of species are reported with pale raphide cells on the surface. These include P. hederaceum and P. warszewiczii. Seeds of some species, e.g., P. anisotomum and P. hederaceum, sometimes have a constriction on the end opposite the funicule.
Philodendron seeds are usually dramatically smaller than those of Anthurium which typically have only two seeds per berry. Seeds of those species of P. subg. Philodendron which were studied (a total of 48 species) ranged from 0.5 mm to 5.0 mm long and averaged 1.67 mm long. Seed diameter ranged from 0.1 to 3.0 mm, averaging 0.7 mm diam. Only a few species have seeds more than 2 mm long. The longest seeds were those of P. scandens and P. hederaceum with seeds 5 mm long. Only a few species have seeds longer than 2 mm. These include P. advena, P. anisotomum, P. findens, P. dolichophyllum, P. grayumii, P. purulhaense, P. rothschuhianum, P. sagittifolium, and P. warszewiczii.
The number of seeds present in each locule is often many fewer than the average number of ovules per locule, presumably owing to the fact that not all are properly pollinated. A careful examination sometimes shows the much smaller undeveloped ovules that were present at the time of flowering. The percentage of ovules in each locule which develop into seeds varies from species to species. Species of P. sect. Calostigma which have only one or a few ovules per locule are more likely to have an equal number of seeds as the number of ovules. On the other hand, species in P. sect. Philodendron, especially those with large numbers of ovules per locule, rarely develop with all the ovules fertilized.
Because species of P. sect. Calostigma have fewer ovules per locule and thus fewer seeds one might expect them to have larger seeds. Though admittedly the sample size was small (only 21 species studied for P. sect. Calostigma and 17 species for P. sect. Philodendron) the unexpected results were that the seeds of species of P. sect. Philodendron in Central America averaged slightly larger than those of P. sect. Calostigma (to 1.69 mm long for P. sect. Philodendron and to 1.66 for P. sect. Calostigma). Seeds are largely pale in color, mostly shades of brown, tan or white. Though for most species mature seed have not been observed, seeds vary in color from medium green (P. rothschuhianum) to white (P. jacquinii and P. panamense), whitish (P. roseospathum), cream (P. schottianum), tan (P. alticola, P. annulatum, P. granulare, P. morii, P. smithii, yellowish and pale yellow (P. brenesii, P. llanoense, and P. strictum), yellow-brown (P. cotonense and P. immixtum), to yellow-orange (P. crassispathum, P. purpureoviride, P. wilburii and P. mexicanum) or pale yellow (P. warszewiczii and P. brenesii), brown (P. ferrugineum), light brown (P. anisotomum, and P. squamipetiolatum), pale brown to tannish brown (P. sagittifolium) and P. squamipetiolatum), or reddish brown (P. heleniae). The dried seeds of two species, P. findens and P. jefense, are described as translucent.