Comparative Morphology and Taxonomy of the Wrangelieae, Sphondylothamnieae, and Spermothamnieae (Ceramiaceae, Rhodophyta)

Abstract

Of 24 species from southern Australia which were previously placed in Wrangelia C. Agardh, only five rightly belong to this genus. A sixth southern Australian species, Wrangelia australis (J. Ag.) comb. nov., is transferred from Bracebridgea J. Ag. Of 12 species referred to Wrangelia from extra-Australian regions, seven are studied and their systematic positions elucidated. Five of the remaining southern Australian species referred to Wrangelia are segregated into three new genera, Shepleya, Wollastoniella, and Drewiana, one into Involucrana Baldock & Womersley, and two into Medeiothamnion Pujals. These genera, probably with Vickersia Karsakoff and Diplothamnion Joly & Yamaguishi, are closely related to Sphondylothamnion Naegeli, and are included in the tribe Sphondylothamnieae Feldmann-Mazoyer. Two new species of this tribe are described from southern Australia. Medeiothamnion lyallii (Harvey) comb. nov. from New Zealand is also transferred from Wrangelia, and Shepleya australe (1. Ag.) comb. nov. from Antithamnion. The remaining 11 species from southern Australia, previously placed in Wrangelia, are found to be conspecific with other species or transferred to other genera not in the tribes studied. The following genera, including four new species, are included in the tribe Spermothamnieae Schmitz: Spermothamnion Areschoug, Tiffanielia Doty & Menez, Ptilothamnion Thuret, Lejolisia Bornet, Lomathamnion gen. nov., Interthamnion gen. nov., and Ptilothamnionopsis Dixon. The monogeneric tribe Wrangelieae, as in species of Ceramiaceae which are considered primitive, forms procarps successively near the apices of potentially indeterminate branches. However, the structure of the cystocarp, in which the gonimoblast is intermingled with sterile whorl-branchlets of the fertile axis, is relatively specialized. The tribes Sphondylothamnieae and Spermothamnieae are closely related, the procarps being restricted to the subapical cell of the fertile axis which may develop from either a potentially indeterminate or a determinate branch. The Sphondylothamnieae are distinguished by the presence of an inner involucrum around the gonimoblast, formed by division of the sterile cells associated with the procarp , and by the presence of whorl-branchlets on axial cells of indeterminate branches. In the Spermothamnieae there is no inner involucrum (except in Lejolisia) and distinct whorlbranchlets are absent from erect axes. These two groups are probably very highly advanced in the Ceramiaceae and not very closely related to the Wrangelieae. Culture studies showed that in both Wrangelia plumosa and Lejolisia aegagropikI the first division of the spore is approximately parallel to the substrate. In L. aegagropila, prostrate axes are produced secondarily by horizontal growth of erect axes. Nuclear studies show that the vegetative cells of the Wrangelieae are uninucleate, while those of the Sphondylothamnieae and Spermothamnieae are multinucleate.