Steven P. Churchill

A CLADISTIC APPROACH TO THE PHYLOGENY OF THE "BRYOPHYTES"

The importance of a cladistic approach in reconstructing the phylogeny of bryophytes is discussed and illustrated by an analysis of the major groups of bryophytes with respect to the tracheophytes and the green algae. The cladistic analysis, using 51 characters taken from the literature, gives the following tentative results: (1) the embryophytes as a whole are monophyletic; (2) the bryophytes (sensu lato) are paraphyletic; (3) the mosses share a more recent common ancestor with the tracheophytes than do the liverworts or hornworts; (4) the hornworts appear to share a more recent common ancestor with the moss-tracheophyte lineage than with the liverworts; however, the existence of several homoplasies makes this placement more problematical; (5) the origin of alternation of generations in the embryophytes, based on out-group comparison with their oogamous, haplontic, algal sister groups, was by progressive elaboration of the primitively epiphytic sporophyte generation; and (6) the presence of vascular tissue (xylem and phloem) can best be interpreted as a synapomorphy of the moss-tracheophyte clade, and tracheids (xylem with ornamented walls) as a synapomorphy of the tracheophytes; therefore, the prevailing designation of “vascular plants” for the tracheophytes alone is inaccurate.

TRANSITION TO A LAND FLORA: PHYLOGENETIC RELATIONSHIPS OF THE GREEN ALGAE AND BRYOPHYTES

Abstract— Separate cladistic analyses of the green algae, liverworts, and hornworts are presented. Classificatory and evolutionary implications of these analyses, in addition to our previously published cladistic analyses of mosses and the embryophytes as a whole, are discussed. The embryophytes are monophyletic, and are part of a larger monophyletic group that includes some of the green algae (the “charophytes”). Important evolutionary transformations in the early phylogeny of the land plants include: (1) retention of the zygote on the haploid plant (gametophyte), with the sporophyte generation arising de novo by delaying meiosis, (2) independent elaboration of an elongate sporophyte in some liverworts, some hornworts, and in the moss‐tracheophyte clade, (3) independent origin of radial (axial) symmetry in the gametophyte in some liverworts and in the moss‐tracheophyte clade, (4) independent origin of leaves on the gametophyte in some liverworts and in mosses, and (5) the unique development of a branching sporophyte with multiple sporangia in the tracheophytes.

The Niobrara River Valley, a Postglacial Migration Corridor and Refugium of Forest Plants and Animals in the Grasslands of Central North America

The Niobrara River Valley of northern Nebraska contains numerous bryophyte, vascular plant, and animal species more typical of forests far to the east, north, and west than to other forests in the grasslands that surround the Valley. Some species are probably relicts of cooler glacial and early postglacial times, when much of what is now grassland was covered by boreal and cool-temperate forests. Others entered the Valley from the east in postglacial times, and some entered from the west as the climate became semi-arid. There is a steep decline in total number of vascular plant species from the mouth of the Missouri River up through the Niobrara Valley, suggesting an environmental gradient and differential migration and extirpation of species at various times since the Pleistocene.AbstraktumDas Niobrara Flusstal nördliches Nebraska enthält viele Laubmoose, Gefässpflanzen, und Tiere Arten, die mehr typisch für ostliche, nördliche, und westliche Wälder sind, als andere Wälder auf der umgebenden Wiesen. Manche Arten sind vielleicht Hinterbliebene von kühleren vergletscherten und frühe nach vergletscheten Zeiten. Andere eintraten ins Tal von Osten während nachvergletscherten Zeiten, und manche eintraten von Westen, während das Klima halb dürr wurde. Es gibt eine steile Neige in die Summe Gefässpflanzenarten von der Mündung des Missouri Fluss bis dem Niobrara Tal, die eine Umgebungsteigung und Unterscheidungswanderung und Ausrottung Arten um verschiedene Zeiten seitdem Pleistozän vorschlagen.ResumenEl Valle del Rio Niobrara, en el norte de Nebraska, contiene un gran número de especies de briofitas, plantas vasculares, y animales que son tipicos de los bosques del este, norte, y oeste de Estado Unidos que de las praderas que rodean al Valle. Alqunas de estas son probablemente vestigios de peridos frios de glaciación y tempranos eventos pos-glaciales, cuando gran parte de lo que es hoy pradera estaba cubierto por bosques boreales y templados. Otras especies entraron al Valle del este en el periodo pos-glacial, y otras entraron del oeste segun el clima se torno semiárido. Hay un alto declive en el número total de plantas vasculares desde le boca del Rio Missouri atravesando el Valle Niobrara, sugiriendo un gradiente ambiental, migración diferencial y extirpación de especies en varias épocas desde el Pleistoceno.

CLADISTICS AND THE LAND PLANTS: A RESPONSE TO ROBINSON

The reconstruction of phylogenetic relationships should be based not on belief but on an explicit and logical analysis of all available characters. Hennigian phylogenetic systematics (cladistics) provides a framework for evaluating putative homologies characterizing particular hierarchical levels, determining relationships of taxa sharing congruent patterns of homologies, and constructing a classification based on this information. Fossils can and should be included in the analysis if enough of the relevant characters are preserved; this is not currently possible for early land plants because of the fragmentary fossil record. To avoid circularity, adaptive and functional considerations should be addressed only after a phylogenetic hypothesis based on patterns on patterns of shared homologies is available.

Clarification and review of Lepidopilum affine and L. grevilleanum (Callicostaceae)

Lepidopilum grevilleanum Mitt., long considered a synonym ofL. affine C. Müll., is a distinct and rare species of western Ecuador.Lepidopilum affine is widespread, presently known from the western and northern Amazon basin, Atlantic region of northern South America, and the Pacific coastal region of Central America. Several new synonyms are proposed forLepidopilum affine: L. allionii Broth.,L. ambiguum Broth.,L. antisanense Bartr.,L. mittenii C. Müll.,L. obtusulum C. Müll., andL. subobtusulum Broth.Lepidopilum pulcherrimum Steere is a synonym ofL. grevilleanum.

TRANSITION TO A LAND FLORA: A REPLY BRENT

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