The Rhachitheciaceae: Revised Circumscription and Ordinal Affinities
1997; American Bryological and Lichenological Society; Volume: 100; Issue: 4 Linguagem: Inglês
10.1639/0007-2745(1997)100[425
ISSN1938-4378
Autores Tópico(s)Lichen and fungal ecology
ResumoThe Rhachitheciaceae, a small family of tropical and subtropical mosses distributed among four genera (Hypnodontopsis, Jonesiobryum, Rhachithecium, and Tisserantiella), are currently placed the Orthotrichales. Two additional genera are here transferred from the Orthotrichaceae to the Rhachitheciaceae, namely Octogonella (= Rhachithecium) and Uleastrum. Furthermore, the genus Rhachitheciopsis is reinstated, and a new genus Zanderia is proposed to accomodate U. octoblepharis. Rhachithecium welwitschii is tentatively considered distinct from R. perpusillum, whereas Uleastrum nitidum is reduced to synonymy with U. palmicola. A key to the 15 species of the Rhachitheciaceae is provided. The single peristome of the Rhachitheciaceae is shown to be an endostome. The architecture of the reduced peristome is reminescent of the Seligeria-type peristome, and is seen as indicative of haplolepideous rather than diplolepideous affinities of the Rhachitheciaceae. The Rhachitheciaceae are a small family established by Robinson (1964) to accommodate two former orthotrichaceous genera: Rhachithecium Le Jol. and Hypnodontopsis Iwatsuki & Noguchi. Rhachitheciopsis P. de la Varde, considered by Iwatsuki (1957) to be closely related to Hypnodontopsis, was reduced to a subgenus of Rhachithecium by Robinson (1964). Recently, Allen and Pursell (1991) transferred the genus Jonesiobryum Allen & Pursell from the Funariaceae to the Rhachitheciaceae, and Zander (1993) excluded the genus Tisserantiella P. de la Varde from the Pottiaceae and suggested that it too clearly belonged to the Rhachitheciaceae. All 12 species, except Rhachithecium perpusillum (Thwait. & Mitt.) Broth. sensu Crum (1956 a,b), are narrowly distributed tropical and subtropical regions of both hemispheres, where they occur on trees. The Rhachitheciaceae have been characterized by spathulate to lingulate, often apiculate vegetative leaves, differentiation of laminal cells into hyaline, rectangular basal cells and chlorophyllose, isodiametric upper cells; a single costa extending to the upper portion of the leaf; lack of a differentiated, cauline epidermis; terminal perichaetia on the stem; and a simple peristome composed of 16 teeth fused into eight pairs (Crum 1993; Zander 1993). As part of a systematic study of the Orthotrichales (Goffinet 1997a), the circumscription and affinities of 27 genera accepted within the Orthotrichaceae have been examined. Goffinet (1997b) recently excluded two genera from the Orthotrichaceae, namely Kleioweisiopsis Dixon (Ditrichaceae) and Trigonodictyon Dixon P. de la Varde (Grimmiaceae), and reduced a third one, Pleurozygodontopsis Dixon into synonymy with Zygodon Hook. Tayl. Here the family is further reduced and the genera Octogonella and Uleastrum are transferred to the Rhachitheciaceae. In order to better understand the relationship of the Rhachitheciaceae to the Orthotrichaceae, material of most taxa has been examined. The taxonomic and systematic implications of these observations are presented here. RHACHITHECIOPSIS P. de la Varde, Bull. Soc. Bot. France 73: 74. 1926. Potier de la Varde (1926) proposed this new genus to accomodate three Rhachithecium-like specimens from Africa that differed from the sympatric R. perpusillum (as R. transvaliense C. Mill.) by the 1 Present address: Botany Department, Duke University, P.O. Box 90339, Durham, NC, 27708 U.S.A. e-mail: goffinet@duke.edu 0007-2745/97/425-439$1.65/0 This content downloaded from 157.55.39.78 on Sat, 25 Jun 2016 05:52:01 UTC All use subject to http://about.jstor.org/terms 426 THE BRYOLOGIST [VOL. 100 seta that is completely curved downward when young or moist and strongly curved into an 's'-like shape when dry, and poorly perichaetial leaves (Potier de la Varde 1926). Iwatsuki (1957) retained Rhachitheciopsis as distinct and suggested close affinities with Hypnodontopsis based on Potier de la Varde's tentative description of mitrate calyptrae. I have seen several calyptrae the type specimen of Rhachitheciopsis, and although fully developed, they appear clearly cucullate. Furthermore, the genus Hypnodontopsis now includes a second species, H. mexicana (Th6r.) Robinson, that differs from the type species by several characters, including the cucullate calyptrae (Robinson 1964). The shape of the calyptrae thus fails to be unambiguously informative addressing the generic relationship of Rhachitheciopsis. Iwatsuki (1957) further emphasized that both Rhachitheciopsis and Hypnodontopsis the anatomy of the seta, immediately below the capsule is strongly asymmetric, due to heavy eccentric thickening of the cell walls on one side of the seta (Iwatzuki 1957; Fig. li). I have examined the anatomy of the seta immediately below the urn Rhachithecium perpusillum (Chang Jinkun 1748-3-ALTA) and R. papillosum (holotype-NY) and both cases the thickenings are also unilaterally heavier, suggesting that this character may be shared by taxa with strongly curved seta (see also below under Uleastrum and Zanderia). The inner surface of the peristome teeth of Rhachitheciopsis tisserantii lacks the palisade-like markings typical of Hypnodontopsis (Fig. 2a,b, 3e,f). In their architecture and ornamentation, the peristome teeth of Rhachtheciopsis (Fig. 2a-b) are similar to those of Rhachithecium (Fig. 3c,d). Scattered additional divisions the outer layer resulting three or four cells (Fig. 2a) per tooth pair have also been observed species of Rhachithecium, as well as other taxa such as Glyphomitrium (Brotherus 1925), and do seem be taxonomically informative. Potier de la Varde (1926) described the teeth as minutely papillose. SEM observation, however, reveals that the teeth are smooth on the outer surface and at most minutely corrugate on the inner surface, as they are Rhachithecium (Fig. 3c,-d). Iwatsuki (1957) described the costa of Hypnodontopsis apiculatus as in midleaf with two layers of stereid cells and one layer of large, thin-walled ventral cells, at the basal portion of the leaf with two layeirs of thick-walled cells, .. . I have only seen one specimen of H. apiculatus (Musci Japonici Exsiccati 1425--ALTA). Here the costa definitely has adaxial substereids, as H. rnexicana (Arsine 4793-NY; Robinson 1964). The costa of Rhachitheciopsis lacks these ventral stereids and is more reminiscent of the costa of Rhachithecium (see below). The capsules of Rhachitheciopsis and Rhachithecium are globose to cup-shaped, whereas Hypnodontopsis the capsule is more elongate and cylindric. This suite of evidence thus supports Robinson's (1964) hypothesis that Rhachitheciopsis is more closely related to Rhachithecium than to Hypnodontopsis. Robinson (1964) considered Rhachitheciopsis and Rhachithecium indistinguishable at the generic level, and rejected a distinction based on the shape of the operculum and the differentiation of the perichaetial leaves, two characters he considered unusually subject to variation this group. As a result he transferred Rhachitheciopsis tisserantii to Rhachithecium, where he placed it its own subgenus distinct from subgenus Rhachithecium by the smooth calyptra, the not noticeably differentiated perichaetial leaves, and the nearly flat operculum. I have examined the three collections of Rhachitheciopsis held PC and all three, the opercula are slightly convex and smooth (i.e., without a rostrum or a mammilla) and the perichaetial leaves are sheathing the seta despite being as long as the seta. Furthermore, the calyptra is definitely smooth Rhachitheciopsis, compared with a scabrous surface Rhachithecium (Crum 1956a; Iwatzuki 1957; Williams 1914). This study also revealed additional characters that separate Rhachitheciopsis tisserantii from species of Rhachithecium sensu stricto. The costa Rhachithecium is weak, with only two bands of substereids, while Rhachitheciopsis tisserantii the costa is strong due to the presence of several layers of substereid bands (Fig. Id; see also Iwatzuki 1957 Robinson 1964). The annulus of Rhachitheciopsis is composed of two layers (not one as described the protologue; Fig. ig), whereas Rhachithecium the annulus is simple (Williams 1914; Iwatzuki 1957; Crum 1993) except maybe for R. brasiliense (Brotherus 1925; synonymized with R. perpusillum by Crum 1956a), and R. welwitschii (see below). Finally, the spore surface R. tisserantii is conspicuously striate (Fig. 2c), while that R. perpusillum and R. papillosum appears pitted (Fig. 2d), perhaps resulting FIGURE 1. Rhachitheciopsis tisserantii. a. Vegetative leaves. -b. Upper laminal cells. -c. Basal laminal cells. -d. Transverse section of costa at midleaf. -e. Transverse section of stem. -f. Calyptra. -g. Annulus. -h. Perichaetial leaves. -i. Transverse section of seta immediately below urn. -j. Capsule, habit when dry (Tisserant 247--PC). Scale bar = 0.2 mm (a, f, h), 20 im (b, c, d, e, g, i) and 70 im (j). (lectotype-PC unless otherwise noted). This content downloaded from 157.55.39.78 on Sat, 25 Jun 2016 05:52:01 UTC All use subject to http://about.jstor.org/terms 1997] GOFFINET: RHACHITHECIACEAE 427
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