A. weberbaueri  Engl.

Only A. lentii has been counted with apparently 2N = 30, since Sheffer & Kamemoto (1976) found a aneuploid series of 2N = 28, 29, 30 and 3 1. Little about crossability is known about this section, however fruit set has been obtained in a cross of A. nymphiifolium C. Koch & Bouché (section Calomystrium ) x A. lentii.

V. PACHYNEURIUM Schott (Fig. 6-8)
This large section recently revised by Croat (1991) comprises principally the "birds-nest" Anthuriums, and is seemingly a very natural one. Most have a decidedly rosulate habit with short, densely rooted stems and generally large blades which are more or less oblanceolate or obovate (broader above the middle) (Fig. 6). Unlike section Porphyrochitonium which may primary lateral veins joining into one or more pairs of collective veins, section Pachyneurium  generally has blades with most of the primary lateral veins extending free to the margin. The species in the section typically have short petioles. The most definitive characteristic of section Pachyneurium is the presence of involute leaf vernation (the manner in which the blade is rolled or folded before opening). In all other sections of Anthurium  (indeed all other Araceae except the Asian genus Lagenandra),  the leaf vernation type (or more appropriately ptyxis) is supervolute, i.e., one margin is rolled inward with the other rolled around it so that a section in end view would look coiled like that of a conch shell. In the section Pachyneurium  both margins are rolled inward toward the midrib. In an end view one would see two tightly rolled portions of leaf. Even in face view the involute vernation is easily observed for the brief time that a leaf is emerging (Fig. 7). This character is important because a few members of the section, such as A. ranchoanum (Fig. 7),A. standleyi (Fig. 8) and A. schottianum have long petioles and other have cordate blades (Fig. 8). These species (especially the latter) do not look much like typical "bird's-nest" anthuriums.

Owing to their ability to accumulate debris and because of their numerous roots, many species of the section are adapted for growing in areas of low rainfall or where there is a pronounced dry season. Members of this section rarely occur in the wettest type of forest soch as in the Chocó Department of Colombia.

Chromosomally the section Pachyneurium is relatively uniform with most species counted having 2N = 30. A few species however have 2N = 60 and B chromosomes have been reported in two other species, A. crenatum  and A. solitarium. Anthurium jenmanii is unique with 2N = 48; a chromosome number otherwise found only in section Tetraspermium .

Typical members of the section include A. affine  Schott, A. crassinervium (Jacq.) Schott, A. cubense  Engl., A. salviniae Hemsley and A. schlechtendalii Kunth. Atypical members with cordate blades and long petioles include A. ranchoanum Engl., A. schottianum  Croat & Baker and A. standleyi  Croat & Baker.

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