Monograph of the Neotropical Fern Genus Polybotrya (Dryopteridaceae)

Description

The genus Polybotrya (Dryopteridaceae) includes 35 species of neotropical ferns. It is distinguished by 1) strongly dimorphic leaves with fertile leaves that resemble skeletons of the sterile, photosynthetic ones; 2) usually high-climbing stems that are covered with scales; and 3) a unique stem anatomy with 5 to 12 circularly arranged meristeles, each surrounded by a black sclerenchymatous sheath, with numerous tiny leaf traces arching between adjacent meristeles. The center of diversity of the genus is the Andes, where 23 species occur, 12 of which are endemic. The coastal mountains of southeastern Brazil are notable because they contain 5 species, all endemic. The range of Polybotrya is from Chiapas, Mexico, southward through Central America; the West Indies; northern South America southward along the Andes to Bolivia and Paraguay and eastward to the Guiana Highlands; the Amazon River basin and the Matto Grosso; and southeastern Brazil. Species of the genus typically inhabit wet, shaded, primary tropical forests from sea level to 2500 m, most often occurring at middle altitudes between 500 and 2000 m. Polybotrya is divided into three subgenera: 1) Soromanes, leaves simply pinnate and veins anastomosing; 2) Sorhifolia, leaves simply or twice pinnate and veins free, close, and parallel; and 3) Polybotrya, leaves decompound and veins free. Polybotrya cervina, a species usually included in Polybotrya, is removed to the monotypic genus Olfersia (Moran 1986). Polybotrya is related to dryopteroid genera such as Arachniodes, Cyclodium, Maxonia. Olfersia, and Polystichopsis. Carl Christensen, the father of modem fern taxonomy, observed (1916) that Polybotrya may have arisen from Maxonia because both have high-climbing stems and strongly dimorphic leaves. The morphological and anatomical evidence presented here suggests that Polybotrya may have evolved instead from a Cyclodium-like ancestor. I chose Polybotrya for study because two aspects of the genus immediately intrigued me: its strongly differentiated sterile and fertile leaves and its long, creeping hemiepiphytic stem (Fig. 1). Since these features evolved separately in unrelated fern genera, studying Polybotrya might well provide insight into broader questions of fern evolution. Polybotrya was suited to monographic study because the number of species (35), all of which are neotropical, was manageable. Finally, no previous monographic work had been done on Polybotrya and many problems of nomenclature and identification remained to be solved.