BLADE SHAPE

Most of the morphological variation in leaf shape which exists in the genus actually occurs among the Central American species of P. subg. Philodendron. The only blade shapes of Philodendron not exhibited by Central American species are those seen on P. goeldii Barroso in P. subg. Meconostigma, which has blades reniform in outline and pedately compound and those of members of P. sect. Schizoplacium which have blades pinnately lobed with a few, prominently falcate divisions. While P. subg. Pteromischum has distinctive leaves (even discounting the winged petiole on adult plants which is definitive, their overall shape and size is matched by other species of P. subg. Philodendron. Blade shape in P. subg. Philodendron relates in some cases to sectional differences. For example, species with three-lobed blades are either members of P. sect. Tritomophyllum or P. subsect. Bulaoanum. Pinnately lobed species are members of P. sect. Polytomium. Alternatively some sections, especially P. sect. Philodendron and P. sect. Calostigma, are highly variable in blade shape, with those of P. sect. Philodendron ranging from oblong to variously ovate to ovate-sagittate and those of P. sect. Calostigma ranging from oblong to subcordate, prominently cordate, cordate-sagittate or even 3-lobed. Philodendron subsect. Belocardium, relatively common in Central America, has more or less oblong, frequently subcordate or cordulate blades. See also section on "Discussion of Subgeneric Classification" for additional details.

While lobed leaves in some Araceae, e.g., Monstera, is due to necrotic processes in which growth stops and tissue rots away (Madison, 1977), the lobed leaves of Philodendron is due to differential growth of leaf tissue.

A listing of the various blades shapes exhibited by Central American species with the number of species which have this leaf shape follows:

ovate (non-cordate) 1

ovate to narrowly ovate 1

narrowly ovate (non-cordate) 8

narrowly ovate to ovate-elliptic 1

broadly ovate to weakly subcordate 1

ovate-cordate 22

broadly ovate-cordate 11

narrowly ovate-cordate 3

ovate-cordate to broadly ovate-cordate 1

ovate-cordate to ovate-sagittate 1?

narrowly ovate-sagittate 1

ovate-subcordate 1

ovate-triangular or triangular-ovate (with posterior lobes) 11

narrowly ovate-triangular 1

ovate to ovate-triangular 5

narrowly triangular 1 (lacking posterior lobes)

triangular-sagittate 1

triangular-sagittate to ovate 1

triangular-sagittate to triangular-hastate 1

sagittate 1

ovate-oblong 2

oblong to oblong-ovate 1

oblong 4

oblong-lanceolate 1

oblong-elliptic 1

oblong-elliptic to oblong-oblanceolate 2

oblong-elliptic to narrowly oblanceolate-elliptic 2

oblong-elliptic to ovate 1

elliptic to oblong-elliptic 1

linear to oblanceolate 1

3-lobed 5

pinnately lobed 2

pinnately lobed to bipinnately lobed 1

In Central America more species have ovate-cordate blades than any other shape. In all variations, 38 species have some sort of ovate-cordate leaf blade. Species with ovate to ovate-triangular leaves are most abundant among P. subg. Philodendron in Central America. At least 55 species have leaf blades with well developed posterior lobes, including those which are cordate, sagittate and hastate. Only 15 species have non-cordate blades which are prominently longer than wide. Eight species have lobed blades with six of these trilobed and two pinnately lobed. Trilobed species are P. anisotomum, P. cotobrusense, P. madronoense, P. rothschuhianum, P. tripartitum and P. angustilobum. Pinnately lobed species are P. radiatum and P. warszewiczii.