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The Systematic Position of Adelothecium Mitt. and the Familial Classification of the Hookeriales (Musci)

1989; American Bryological and Lichenological Society; Volume: 92; Issue: 3 Linguagem: Inglês

10.2307/3243392

1938-4378

Alan T. Whittemore, Bruce Allen,

Lichen and fungal ecology

On the basis of its intricately pinnately branched rhizoids, dark-red, opaque stems, strong single costa, and long axillary hairs Adelothecium is aligned with the genera of the Hookeriales. Within the the genus appears isolated because of the presence of pseudoparaphyllia, the more or less unfurrowed exostome teeth, the production of gemmae on reduced axillary branches, and the insertion of the rhizoids well below the leaves or around the periphery of buds. An evaluation of gametophytic and sporophytic features within the Hookeriales indicates that two groups, distinct at family level, are present: The Daltoniaceae (consisting of the genera Achrophyllum, Adelothecium, Bryobrothera, Calyptrochaeta, Crosbya, Cyathophorum, Cyathophorella, Daltonia, Distichophyllidium, Distichophyllum, Leskeodon, and Leskeodontopsis), and the Hookeriaceae (consisting of Actinodontium, Amblyotropis, Brymela, Callicostellopsis, Crossomitrium, Cyclodictyon, Diploneuron, Helicoblepharum, Hemiragis, Hookeria, Hookeriopsis, Hypnella, Lepidopilidium, Lepidopilum, Leucomium, Philophyllum, Pilotrichidium, Rhynchostegiopsis, Sauloma, Schimperobryum, Schizomitrium, Stenodesmus, Stenodictyon, Tetrastichium and Thamniopsis). The Cyathophoraceae, Distichophyllaceae and Adelotheciaceae are considered synonymous with the Daltoniaceae, while the Leucomiaceae is placed in the synonymy of the Hookeriaceae. The presence of a central duct in the stem of Dendrocyathophorum indicates that it should be placed in the Hypopterygiaceae. The genus Adelothecium Mitt. consists of a single species, A. bogotense (Hampe) Mitt., native to the American tropics and Madagascar (Crosby 1976). Except for Miiller (1900), who treated it as a subgenus of Distichophyllum Dozy & Molk., the genus has been universally recognized for over a century. Earlier authors placed it in a broadly defined family Hookeriaceae (Bartram 1949; Brotherus 1925; Mitten 1869; Welch 1976), but it differs from Hookeria J. E. Sm. and its relatives in several characters, and more recent authors have disagreed about its proper familial placement. The genus was first removed from the Hookeriaceae by Miller (1971). He divided the Hookeriaceae s.l. into several families, placingAdelothecium in a new family (Distichophyllaceae Miller) mainly because of its asymmetrical, complanate leaves, single strong costa, and unstated characters of the peristome. He considered the Daltoniaceae Schimp. to be closest to his Distichophyllaceae, but also suggested that three small families, Ephemeropsaceae Schultze-Mot., Hypopterygiaceae Kindb., and Cyathophoraceae Miller, might also be related to these families. Miller's realignments were not accepted by Crosby (1974), who pointed out the heterogeneity of Miller's families with respect to peristomial characters. Crosby reunited most of Miller's new families and returned Adelothecium to the Hookeriaceae, aligning it with Crosbya Vitt (as Bellia) in an 0007-2745/89/261-272$1.35/0 This content downloaded from 207.46.13.124 on Wed, 22 Jun 2016 05:43:01 UTC All use subject to http://about.jstor.org/terms 262 THE BRYOLOGIST [VOL. 92 informal Most of the other genera Miller placed in his Distichophyllaceae and Daltoniaceae were treated by Crosby in the adjacent group in the Hookeriaceae, but four genera showing a different peristome structure (see below) were treated as a group in a separate family, Daltoniaceae. The latter family also included many genera that gametophytically resemble other groups of Hookeriaceae. Norris and Robinson (1979) pointed out that Bryobrothera Th6r., placed by Brotherus (1924) in the eubryalean family Rhizogoniaceae, belongs among the Hookeriales. While accepting Crosby's familial treatment, they considered Bryobrothera to be intermediate between his adelothecioid and distichophylloid groups and suggested uniting the two. Recently Buck (1987, 1988) rejected the schemes of Miller and Crosby. Believing peristomial reduction to be rampant in the group, he reunited most of the distichophylloid, adelothecioid and daltonioid genera in a redefined family Daltoniaceae. However, he treated Adelothecium as a monotypic family, Adelotheciaceae Buck, distinguished chiefly by the production of gemmae on reduced axillary branches and the many-celled, hyaline axillary hairs. He treated Adelotheciaceae as a sister to his Daltoniaceae. He noted that Bryobrothera shares characters with Adelothecium and suggested that the two might prove to belong together despite the rhizoidal gemmae and few-celled, basally pigmented axillary hairs of Bryobrothera. THE RELATIONSHIPS OF ADELOTHECIUM The characters of Adelothecium that seem most useful in aligning it within the Hookeriales are its intricately pinnately branched rhizoids, dark-red, opaque stems, strong single costa, and axillary hairs, which are several cells long and have the basal cell hyaline. These characters place it with a of genera (henceforth called the unicostate Hookeriales), which may be broadly defined to include Achrophyllum Vitt & Crosby (= Pterygophyllum Brid.), Bryobrothera, Calyptrochaeta Desv. (= Eriopus Brid.), Crosbya, Cyathophorum P. Beauv., Cyathophorella (Broth.) Fleisch., Daltonia Hook. & Tayl., Distichophyllidium Fleisch., Distichophyllum, Leskeodon Broth., and Leskeodontopsis Zant. Within the Hookeriales, character-state variation is large, but the different characters are not well correlated with one another (Table 1), The gametophores are essentially unbranched (except for the sexual branches) in most of the group, but are sparingly branched in Adelothecium and in some species of other genera, especially Achrophyllum and Calyptrochaeta. The stems are uniformly deeply pigmented in most of the genera, but the pigmentation may be confined to the base of the stem in Achrophyllum, Calyptrochaeta, and Cyathophorella; in Achrophyllum and Calyptrochaeta the entire stem is sometimes unpigmented. The internal structure of the stem is quite variable. In the most common stem structure within the Hookeriales, the inner cortical cells are large and thin-walled while the outer cortical cells are smaller and have thick pitted walls. This stem structure is found in Adelothecium, Calyptrochaeta, Cyathophorella, Cyathophorum, Leskeodon, Leskeodontopsis, and in some species of Achrophyllum and Distichophyllum. In Bryobrothera and other species of Distichophyllum the cortical cells are small and thick-walled throughout. The stems of Daltonia and Crosbya are intermediate in structure, the inner cortical cells being somewhat larger than the outer and with the walls thinner but still distinctly thickened. Lastly, in some species ofAchrophyllum the cortical cells are large and lax throughout, with only poorly developed wall thickenings in the outer cortex. Most genera have no central strand in the stem, but a central strand is present in Achrophyllum, Cyathophorella, and Cyathophorum. A distinct hyaloderm is formed only in Achrophyllum. Rhizoid structure and position are also variable within the group. Rhizoids are densely clustered proximal to leaf bases in Crosbya, Distichophyllidium, and some species of Daltonia and Distichophyllum, but are scattered over the cortex, usually near the base of the stem, in Calyptrochaeta, Achrophyllum, Cyathophorum, and Cyathophorella. In Adelothecium rhizoids are clustered well away from the leaf insertion or at the periphery of vegetative buds (Fig. 1). Bryobrothera produces relatively few rhizoids; Norris and Robinson (1979) state that its rhizoids arise from scattered cortical initials, but we have been unable to confirm this because of the opacity of the stem. In Leskeodon, most species of Daltonia, and a few species of Distichophyllum, the stems are and rhizoids are formed only at stem bases. The rhizoids are 2-3 pinnately branched in most of the genera (Fig. 3-4, 6), but are rather sparingly branched in Daltonia, Leskeodon, and the short stemmed (see below) within Distichophyllum. In Crosbya the rhizoids are unbranched. The axillary hairs are 3-7 cells long in most species. However, axillary hairs are only 2 cells long in a few species of Achrophyllum and Calyptrochaeta, and may reach at least 10 cells in length in Adelothecium (Fig. 10-12). The basal cell (sometimes several cells) of the axillary hair typically becomes brown in Bryobrothera, Crosbya, Cyathophorella, Cyathophorum, and Daltonia, but the entire hair remains hyaline in Achrophyllum, Adelothecium, This content downloaded from 207.46.13.124 on Wed, 22 Jun 2016 05:43:01 UTC All use subject to http://about.jstor.org/terms 1989] WHITTEMORE & ALLEN: ADELOTHECIUM AND HOOKERIALES 263 TABLE 1. Distribution of selected character states within Daltoniaceae.