Woodwardia is a genus of fourteen species of temperate to subtropical, terrestrial ferns characterized by: (1) short- to long-creeping stems that are neither trunk-forming nor scandent; (2) pinnatifid to pinnate-pinnatifid fronds; (3) stipes having two prominent adaxial vascular bundles with 0-6 lesser abaxial vascular bundles; (4) anastomosing venation in trophophylls to form a row of =F1 uniformly shaped, quadrilateral areoles oriented parallel to the major axes of the fronds ("primary areoles"), with further =F1 irregular venular anastomses ("secondary areoles") but with the veins ultimately ending freely at the laminar margin; (5) indument comprising a mixture of lax, non-clathrate brownish to orangish scales and capitate, multicellular glands, at least in the early stages of frond emergence; (6) discrete sori, one per areole, arranged in uniseriate rows along the primary areoles of the sporophylls; (7) a generally conduplicate indusium; and (8) a base chromosome number of 34 or 35. Phylogenetic analysis of a morphological data set of 37 informative characters indicate that characteristics 4, 6, 7 and 8 uniquely distinguish Woodwardia as a monophyletic group that is sister to the remaining clades within the Blechnaceae. Thus defined, Woodwardia includes the segregate genera Anchistea, Chieniopteris, and Lorinseria, comprises two major monophyletic subclades: subgenus Woodwardia and subgenus Lorinseria. Chain ferns today are distributed interruptedly throughout the northern hemisphere with centers of diversity in eastern Asia and North America. Representatives of each major clade are either extant or have been found as fossils exclusively in North America, Europe and/or Asia, suggesting that the genus evolved and diversified prior to the breakup of Laurasia. The Arcto-Tertiary distribution of both fossil and extant species of Woodwardia is unique within the Blechnaceae, which otherwise exhibit a Gondwanan distribution in the temperate and montane tropical regions of Africa, South America and Australasia. The ample and widely distributed fossil record of Woodwardia, which makes a definitive first appearance in the Paleocene, suggests that members of the genus were important and characteristic elements of warm temperate and subtropical Arcto-Tertiary Forests. Further, the combination of modern biogeographic data with the appearance derived morphologies early in the Tertiary suggests that Woodwardia underwent a period of rather rapid evolution and radiation followed by range disruption and extirpation of evolutionary lines to produce both the diversity and distribution of species as we find them today, a pattern which may have parallels with other leptosporangiate ferns that were more widespread as fossils and which have maintained "static" morphologies for tens of millions of years (c.f. Onoclea).

Key words: biogeography, Blechnaceae, ferns, phylogeny, systematics, Woodwardia