This revision is based on more than 25 years of field studies in Central and South America, between 1967 and 1993. All but 15 of the 95 species were studied live in the field or under cultivation at the Missouri Botanical Garden. Those not studied live include the following: P. breedlovei, P. brewsteriense, P.

chirripoense Croat & Grayum, P. cotobrusense, P. dwyeri, P. folsomii, P. hammelii, P. jefense, P. madronoense, P. roseospathum var. angustilaminatum, P. sousae, P. ubigantupense, P. utleyanum, and P. verapazense Croat. Except for these, all descriptions have been prepared from both living and dried specimens. The use of ("dried") preceding all or any part of the description is an indication that all that follows is based on herbarium material only. Morphological characters were coded directly into a computerized database to ensure parallel and sortable descriptions. The aroid descriptions database, completely rewritten since the publication of my last revision, Anthurium sect. Pachyneurium (Croat, 1991), contains 892 character states that are used to describe the morphological diversity expressed in Philodendron. A total of 108 of these are used exclusively for description of the bisexual inflorescence (and thus were not used in the descriptions of Philodendron) while 220 describe unisexual inflorescences. The database also allows for sorting of characters for use in writing keys or in providing useful lists of characters for preparing a cladistic survey. In addition, the database can be put to future use for the preparation of floristic surveys or for adding additional newly discovered species. The description database is tied directly to the nomenclatural database in Tropicos (Crosby, 1986; Crosby & Magill, 1986). Finally, discussions and references to illustrations as well as exsiccatae are stored separately but tied to a particular species description and to the nomenclatural information by a unique taxon number. Specimens can be added to the exsiccatae up almost until the time of publication because they are automatically presorted to localities before being printed. Species descriptions are decoded into narrative text automatically before final editing for style.

Terminology and usage in the descriptions in this revision are largely defined by Croat & Bunting (1979). Two notes concerning measurments of parts not mentioned in the above work are that blade length is measured from the apex to the tip of the posterior lobes, not at the petiole insertion. The length of the posterior lobes are measured from the apex of the petiole to the most distant part of the posterior lobe not to the apex of the sinus. The sinus is measured from an imaginary line across the tips of the posterior lobes to the apex of the petiole.

The colors reported in the description frequently are taken from the color chart by Berlin & Kay (1969) and are referenced in the text as B & K. This color chart, available from the University of California Press, is a reproduction of the Munsell Color Array of 40 hues, at maximum saturation, with nine degrees of brightness. This represents 40 hues in the vertical columns and nine degrees of brightness in the horizontal columns. Colors are arranged in 10 basic clusters with four different hues per cluster, ranging from red through yellow, green, blue, purple and finally red-purple. The four columns for each color cluster are numbered 2.5, 5, 7.5, and 10. These numbers are repeated for each basic color type. The colors from the B & K color chart are read by first reporting the color, then the row followed by the column. For example, the third color in the fifth row is Red 5/7.5. The second color in the eighth row is Red 8/5.

Ecological zones, though sometimes estimated from my own experience with Central American vegetation, are largely taken from Holdridge lifezone maps (Holdridge, 1967; Holdridge et al., 1971) where they exist for Central American countries and for Mexico from the "Mapa de tipos de vegetación de la Repúplic de Mexico" (Flores, et al. 1971). The Holdridge Life Zones included in Central America and in areas where Philodendron occurs are listed here. Each life zone is represented also by an abreviation and it is this abreviation which appears on the life zone maps. They are arranged in a generally dryer to generally wetter order. The zones are as follows: Tropical dry forest (T-df); Tropical moist forest (T-mf), Premontane wet forest (P-wf), Tropical wet forest (T-wf), Lower montane rain forest, Premontane rain forest, pluvial forest, etc. Note: This has been modified.

Herbarium material has been widely distributed and original field vouchers are cited for all herbaria whose material was seen. Herbarium material may consist of one of three kinds: (1) complete original sets (wild collected); (2) sterile original material with an inflorescence added from a cultivated plant of the same number; and (3) material collected entirely from the cultivated plant. Specimens based entirely or in part on cultivated material are clearly indicated on the herbarium label.

Herbarium specimens were borrowed from most major herbaria including: AAU, B, BBS, BISH, BM, BR, CAS, CAY, CM, COL, CR, DAV, DUKE, DS, EAP, ECON, ENCB, F, FLAS, FSU, FTG, G, GH, HBG, ISC, K, L, LA, LL, LE, M, MEXU, MICH, NY, PMA, RSA, S, SCZ, SEL, TEX, U, UC, UMO, US, VEN and WIS.

Descriptions are mostly parallel and as complete as possible. Descriptions of the pistils, so vitally important in the suprageneric classification of Philodendron, are particularly detailed. In order to avoid repetition, description references are made to Style Types discussed in a portion of a Ph.D. thesis by Simon Mayo (Mayo, 1986). These style types are discussed and illustrated (Fig. 469) in the introduction under the section on "Morphology of Reproductive Structures- Gynoecium".