The section is divided into two series as defined in the following key:

Key to Series of Anthurium Section Pachyneurium

Blades usually oblanceolate to oblanceolate-elliptic, rarely oblong-elliptic or ovate- cordate, usually drying brown, reddish brown, greenish-brown, or blackened, rarely greenish or yellowish-green; primary lateral veins usually spaced and stout (generally more than 3 cm apart), much more conspicuous than the interprimary veins (the latter usually lacking); fruits usually red or purple to purplish in South America, often orange in Costa Rica and Panama; found throughout the range of the section.
seriesPachyneurium

Blades usually oblong-elliptic to oblong-oblanceolate or elliptic, rarely oblanceolate, usually drying green to yellow-green; primary lateral veins usually moderately weak, usually closely spaced (generally less than 3 cm apart); interprimary veins usually many, these almost as conspicuous as the primary lateral veins; fruits mostly orange, sometimes purple; mostly endemic to Equador, also Narino, Columbia to Bolivia.
Series Multinervia

In general where interspecific pollinations have been attempted, the species of section Pachyneurium are intercrossable. Several intersectional crosses have been made. Most Central American members of Pachyneurium will interbreed as will most South American members of the section but few Central and South American species crosses were viable (Croat, 1991). Fruit set has been obtained in some intersectional crosses involving section Belolonchium (A. umbrosum Liebm. x A. standleyi Croat & Baker; A. chiapasense  Standi. x A. atropurpeum  Schultes & Maguire and A. lancetillense Croat (ined.) x A. luteynii  Croat. Additionally A. hookeri Kunth (unidentified section) is crossable with both A. crenatum and A. luteynii .

VI. POLYPHYLLIUM Engl. (Fig. 9 & 10)

This small but very natural section has only 2 species. It is characterized by having very slender, wiry stems with adventitious roots along the internodes (restricted to the nodes in other sections). In addition Polyphyllium is the only section of Anthurium which lacks cataphylls, having instead sheathing petioles for protection of new growth. The section was revised by Croat & Baker (1978) and includes A. flexile Schott and A. clidemioide Standley. Only one taxon (A. flexile ssp. muelleri (Macbr.) Croat & Baker) has been counted with 2N = 60 chromosomes. The crossability of A. flexile to other Anthurium species is at present unknown.

VII. LEPTANTHURIUM Schott (Fig. 11)
This small section containing perhaps only A. gracile (Rudge) Lindl. is nevertheless unique and apparently quite natural. Anthurium gracile  differs in being perhaps the only species with white roots (owing to a layer of velamen). Sheffer and Kamemoto (1976) were unable to cross A. gracile with any of the other 56 species used in their compatibility studies.

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