A molecular phylogeny of scaly tree ferns (Cyatheaceae)

Abstract

Tree ferns recently were identified as the closest sister group to the hyperdiverse clade of ferns, the polypods. Although most of the 600 species of tree ferns are arborescent, the group encompasses a wide range of morphological variability, from diminutive members to the giant scaly tree ferns, Cyatheaceae. This well-known family comprises most of the tree fern diversity (∼500 species) and is widespread in tropical, subtropical, and south temperate regions of the world. Here we investigate the phylogenetic relationships of scaly tree ferns based on DNA sequence data from five plastid regions (rbcL, rbcL-accD IGS, rbcL-atpB IGS, trnG-trnR, and trnL-trnF). A basal dichotomy resolves Sphaeropteris as sister to all other taxa and scale features support these two clades: Sphaeropteris has conform scales, whereas all other taxa have marginate scales. The marginate-scaled clade consists of a basal trichotomy, with the three groups here termed (1) Cyathea (including Cnemidaria, Hymenophyllopsis, Trichipteris), (2) Alsophila sensu stricto, and (3) Gymnosphaera (previously recognized as a section within Alsophila) + A. capensis. Scaly tree ferns display a wide range of indusial structures, and although indusium shape is homoplastic it does contain useful phylogenetic information that supports some of the larger clades recognised.

Palynological analysis of Sphaeropteris gardneri (Cyatheaceae, Pteridophyta)

“…These results are similar to those observed by other authors for other taxa of the genus (Tryon 1971, Erdtman and Sorsa 1971, Gastony and Tryon 1976, Liew and Wuang 1976, Braggins and Large 1990, Tryon and Lugardon 1991, Conant et al 1996, Korall et al 2007). …”

“…In these works, Conant et al (1996) and Korall et al (2007) used the spore morphology in order to support the phylogenetic hypothesis.…”

“…Tryon. The distinctive characteristics to differentiate this genus from the rest of the Cyatheaceae is the presence of conform scales at the bases of the petioles (Tryon 1970) and spores with echinate perispore (Korall et al 2007).…”

Rates of ecological divergence and body size evolution are correlated with species diversification in scaly tree ferns

“…89%). Tree fern taxonomy and classification have been problematic and marked by frequent changes in the number and definition of genera [28,34,35]. We adopted a morphological circumscription of clades that is very close to Holttum's [32] system of subgenera and sections within a universal Cyathea, which shows a surprising correspondence with phylogenetic evidence [28 -30].…”

“…Here, we examine the correlation between ecological niche divergence, body size variation and species diversification in the tree fern lineage (Cyatheales, sensu Smith et al [27]), which is the second largest order of extant ferns, with approximately 700 species [27,28]. Among tree ferns, the scaly tree ferns (Cyatheaceae) represent an ideal system to investigate the relative roles of ecological and morphological evolution in the diversification of plant lineages for several reasons: (i) it is a highly diverse Pantropical fern family (approx.…”