Based on a field oriented study of phenology and pollination behavior carried out at La Selva in Heredia Province of Costa Rica, Grayum (1996) reported species of P. subg. Pteromischum flowered for periods of 4-8 weeks. Obviously since most members of P. subg. Pteromischum have only one or two inflorescences per axil versus sometimes 4 or more for P. subg. Philodendron the flowering episodes of the latter might be longer than two months. The flowering events however short or long are not necessarily the same year after year. I suspect that, like understory vegetation, their flowering sequence may be affected by the onset of the rainy season (Croat, 1975).
Based primarily on a phenological study of herbarium collections, flowering (and to a lesser extent fruiting) behavior has been studied for Central American species of P. subg. Philodendron. These studies resulted in a phenological statement for each species. This statement follows the description of each species as a part of the discussion. Some general comments regarding phenology are important.
In studying herbarium material for phenological variation it is often difficult to determine the exact state of the inflorescence. However, with experience it is relatively easy to determine inflorecences which have never opened, i.e., pre-anthesis verus those which have already opened. Spathes which have never opened are very tightly closed whereas those which have already undergone anthesis are not so tightly closed. By dissecting the spathe one can quickly determine if the pollen has emerged. If so the spathe has already opened and reclosed over the spadix.
Spadices which are at anthesis when they are collected are usually easy to discern as well because they are typically opened when pressed. It is difficult, however, to easily predict the age of an inflorescence after anthesis and before considerable swelling with the enlarging of the pistils. Since an inflorescence at anthesis is a rare event (open less than 24 hours in a years time) while every successfully pollinated inflorescence persists for one to many months, there will always be many more collections with "post-anthesis" inflorecences than those described as "in flower".
Central American members P. subg. Philodendron fall into several phenological groups depending on when they flower. All of these categories can have variations and flowering is rarely consistently equal throughout any period. Though some categorizations are tentative these are listed in Appendix 5, Phenological Patterns of Central American Philodendron subg. Philodendron.
The flowering patterns of Central American members of P. subg. Philodendron are as follows:
Flowering in dry-season and wet season
Flowering only in wet season
Flowering only in dry season
Flowering all year