This final chapter concerns epiphyte occurrence in three contexts: global, taxonomic, and ecological. First, global and taxonomic patterns and the question of why epiphyte floras are unevenly developed throughout the tropics are addressed. Second, the effects of climate, topography, and soil fertility on species range and abundance are considered. Finally, hypotheses are offered to explain why certain plant lineages have been more successful than others in forest canopy habitats.

Distribution: taxonomic and geographic

At the higher taxonomic levels, epiphytes are diverse; excluding the mistletoes, 84 families, including 69 in Magnoliophyta, contain qualifying taxa. But rather few major clades account for most of the species; just 23 families harbor about 98% of the total flora in 87% of the epiphytic genera (Tables 1.1, 1.2). Fifteen families include but a single epiphyte; 52% of the 871 epiphytic genera contain five or fewer species, and about half of those contain only one. Heaviest contributors are Araceae, Bromeliaceae, Ericaceae, Gesneriaceae, Melastomataceae, Piperaceae, Orchidaceae, Rubiaceae, and several fern families. Forty-three genera each contain more than 100 epiphytic species (Table 1.2): of the 43, 22 are orchids, 8 are ferns, 4 are bromeliads, 3 are from Aracaceae, and the remaining 6 are contributions from five additional families.

Geographic asymmetry is also considerable, especially in the more advanced taxa (Madison 1977). Of the 86 canopy-adapted fern genera listed by Madison, approximately two-thirds are pantropical; the remainder are divided about equally between the two subregions – 16 exclusively neotropical and 14 paleotropical.