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This section consists of only A. radicans  C. Koch, a species from southeastern Brazil. It is presumably most closely related to section Urospadix . Although no single character distinguishes it from any other section, the combination of characters it exhibits, especially its repent habit and short, more or less ellipsoid spadix, make it unique.

Chromosome counts on A. radicans indicate that there may be more than one ploidy level involved since Pfitzer (1975) reports a haploid count of N = 15, whereas Gaiser (1927) reports a diploid count of 2N = 50. Little is known about crossability in this species.

XIV. CALOMYSTRIUM Schott emend Engl. (Fig. 30-34)
The section Calomystrium is one of the most natural and recognizable groupings within Anthurium however, some of the differences are more easily observed than put into words. Members of the section have generally distinct leaf types, variously cordate (Fig. 30) and generally thick, often variously speckled with light spots on the lower surface but only rarely with dark glandular punctations. More frequently than in any other section, the leaf blades have distinctly visible, short, linear clusters of raphide cells which are paler than the surface but rarely more than a few millimeters long. Probably the most easily observed characteristic of the section is the presence of persistent cataphylls (Fig. 31) which are usually dry reddish- brown to brown and remain intact. In other sections cataplylls are usually either deciduous or weather into fibers.

lnflorescences of section Calomystrium are also distinctive but they are more difficult to describe (Fig. 32-34). In general spadices appear somewhat glossy, the tepals and the spathes are thick and often variously pastel colored, ranging from white to pale green and from pale pink to deep red. Perhaps more than any other group, a higher percentage of the species produce sweet, pleasant aromas.

The group has some very well known examples not the least of which is A. andraeanum  Linden, the most well known species in the genus because of its long use in the cut flower industry. Others include A. formosum Schott, A. hoffmannii Schott (not as of Exotica 111), A. nymphiifolium Koch & Bouché and A. obtusilobum Schott.

Section Calomystrium is a very large one with what would appear to have a large number of new species concentrated especially in Panama, Colombia and Ecuador.

Chromosomally, the section is simply 2N=30. No polyploids have been identified, and B chromosomes have only been found in A. andraeanum  Linden intrasectional hybridizations have been attempted with a number of these species, and they tend to be intercrossable. Specifically, hybrids have been obtained from crosses among A. andraeanum Linden, A. formosum Schott, A. kamemotoanum Croat, A. nymphiifolium C. Koch & Bouché, A. ravenii  Croat & Baker, A. roseospadix  Croat and A. veitchii  Masters.

More intersectional pollinations have been successful with section Cardiolonchium than any other section. Fruit set has been obtained between section Calomystrium and sections Belolonchium , Cardiolonchium , Digitinervium , Polyneurium and Semaeophyllium .