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Published In: Species Muscorum Frondosorum 64. 1801. (Sp. Musc. Frond.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 11/8/2011)
Acceptance : Accepted
Project data     (Last Modified On 11/8/2011)

44. WEISSIA               Plates 59, 60, 6162.

Weissia Hedw., Sp. Musc. 168, 1801. Lectotype: Weissia controversa Hedw. fide Mitten, Kew J. Bot. 8: 258, 1856.

Cavanillea Borkh., Disp. Pl. 251, 1809, hom. illeg. non Medikus, 1787, non Desf. in Lam., 1792.

Subg. Weissia

Simophyllum Lindb., Act. Soc. Sci. Fenn. 10: 74, 1871, nom. illeg. incl. gen. prior.

Rechingerella Fröhl., Ann. Naturhist. Mus. Wien 66: 36, 1962 [1963], hom. illeg. non Petrak. Type: Rechingerella macedonica J. Fröhl.

Weissia subg. Weisia BSG, Bryol. Eur. 1: 5, 1851 (fasc. 47. Consp. vol. 1: VII), nom. illeg.

Weissia subg. Microweisia BSG, Bryol. Eur. 1: 5, 1851 (fasc. 46–47 Consp. vol. 1: VII).

Weissia subg. Euweisia Schimp., Syn. 54, 1860, nom. illeg.

Hymenostomum subg. Weisia (Hedw.) Andrews, Bryologist 23: 31, 1920, nom. illeg. prior. ut gen.

Tortella subg. Nanotortella C. Jens., Danm. Moss. 2: 318, 1923, nom. illeg. incl. typ. gen. prior., p.p.

Bryum sect. Weissia (Hedw.) Relh., Fl. Cantabr. 425, 1802. Type: Bryum virens Relh.

Weissia sect. Controversae Nees & Hornsch., Bryol. Germ. 2(2): 25, 31, 1831.

Weissia sect. Viridulae BSG, Bryol. Eur. 1: 66, 1846 (fasc. 33–36 Mon. 6).

Weissia sect. Euweisia C. Müll., Syn. 1: 651, 1849, nom. illeg.

Didymodon sect. Pusilli Kindb., Eur. N. Amer. Bryin. 2: 272, 1897. Type: Didymodon triumphans (De Not.) Kindb.

Barbula sect. Edentella C. Müll., Gen. Musc. Fr. 453, 1900. Type: Barbula schweinfurthiana C. Müll.

Weissia subsect. Sphalerostomae Nees & Hornsch., Bryol. Germ. 2(2): 24, 25, 1831, nom. illeg.

Subg. Astomum (Hampe) Kindb., Eur. N. Amer. Bryin. 2: 283, 1897.

Astomum Hampe, Flora 20: 285, 1837. Lectotype: Astomum crispum (Hedw.) Hampe fide Margadant, Acta Bot. Neerl. 8: 274, 1959.

Sphaerangium Schimp., Syn. 12, 1860, nom. illeg. incl. gen. prior.

Systegium Schimp., Syn. 30, 1860. Lectotype: Systegium crispum (Hedw.) Schimp.

Astomum subg. Euastomum (C. Müll.) Broth., Nat. Pfl. 1(3): 384, 1901, nom. illeg.

Hymenostomum subg. Astomum (Hampe) Andrews, Bryologist 23: 31, 1920.

Tortella subg. Systegium C. Jens., Danm. Moss. 2: 317, 1923, hom. illeg. Type: Tortella crispa (Hedw.) C. Jens.

Phascum sect. Astomum (Hampe) ångstr. in Fries, Summ. Veg. Scand. 1: 97, 1846.

Weissia sect. Astomum (C. Müll.) C. Müll., Bot. Zeit. 5: 98, 1847, as autonym.

Weissia sect. Systegium Lindb., Öfv. K. Vet. Ak. Förh. 21: 230, 1864. Lectotype: Weissia crispa (Hedw.) Mitt.

Acaulon sect. Macrobryum C. Müll., Linnaea 43: 353, 1882. Type: Acaulon lorentzii C. Müll.

Phascum sect. Systegium C. Müll., Hedwigia 37: 76, 1898, nom. illeg. incl. sect. prior.

Subg. Hymenostomum (R. Br.) Limpr., Laubm. Deutschl. 1: 225, 1886, as autonym.

Hymenostomum R. Br., Trans. Linn. Soc. London 12(2): 572, 1818. Type: Hymenostomum microstomum (Hedw.) R. Br.

Gymnostomum subg. Hymenostomum (R. Br.) Schimp., Syn. 33, 1860.

Mollia subg. Hymenostomum (R. Br.) Lindb., Musci Scand. 21, 1879.

Weissia subg. Hymenostomum Limpr., Laubm. Deutschl. 1: 225, 1886, nom. illeg.

Hymenostomum subg. Kleioweisia Limpr., Laubm. Deutschl. 1: 224, 1886. Type: Hymenostomum rostellatum (Brid.) Schimp.

Weissia subg. Hymenostomum (R. Br.) Kindb., Eur. N. Amer. Bryin. 2: 283, 1897, nom. illeg.

Hymenostomum subg. Euhymenostomum Andrews, Bryologist 23: 31, 1920, nom. illeg.

Weissia sect. Hymenostomum (R. Br.) BSG, 1: 56, 1846 (fasc. 33–36 Mon. 6), as autonym.

Hymenostomum sect. Microstoma B.&S. in BSG, Bryol. Eur. 1: 56, 1846 (fasc. 33–36 Mon. 6), nom. illeg. incl. typ. gen. Type: Hymenostomum microstomum (Hedw.) R. Br.

Hymenostomum sect. Tortilia B.&S. in BSG, Bryol. Eur. 1: 56, 1846 (fasc. 33–36 Mon. 6). Type: Hymenostomum tortile (Schwaegr.) B.&S.

Weissia sect. Hymenostomum (R. Br.) C. Müll., Syn. Musc. 1: 660, 1849.

Mollia sect. Hymenostomum (R. Br.) Braithw., Brit. Moss Fl. 1: 230, 1885.

Subg. Phasconica (C. Müll.) Zand. see below.

Phasconica C. Müll., Linnaea 43: 438, 1882. Type: Phasconica lorentzii C. Müll., lectotyp. nov.

Subg. Pseudopottia Kindb., Eur. N. Amer. Bryin. 2: 283, 284, 1897.

Sect. Gymnostomum Mitt., J. Linn. Soc. Bot. 12: 41, 129, 131, 1869.

Sect. Tortularia Mitt., J. Linn. Soc. Bot. 12: 15, 130, 139, 1869.

Subsect. Hapalostomae Nees & Hornsch., Bryol. Germ. 2(2): 24, 25, 1831.


            A large genus found on all continents except Antarctica, mostly growing on soil.

Notes:           Weissia is superficially not well distinguished from Trichostomum. Andrews (1945) felt that the Weissia complex should be “extended to cover Trichostomum.” In Weissia, the central strand nearly universally present (Pl. 59, f. 2; 62, f. 7) at least in the specimens examined), upper laminal margins are usually narrowly and sharply incurved (Pl. 59, f. 7; 60, f. 5) as is the case with Chionoloma and Weissiodicranum (those of Weissia termitidarum and certain others are loosely involute), the upper laminal cells are often more strongly bulging ventrally than dorsally (although usually overlain with papillae), the hydroid strand is usually absent (but present in W. controversa), the sexual condition is commonly monoicous (position of antheridia often varying between or within collections of a particular species), perichaetial leaves are often larger than the cauline, peristomes are generally short with the teeth more or less flattened (Pl. 59, f. 9–10) or absent, and spores are rather large, 14–28 µm in diameter. When present, the ventrally colliculate condition, i.e. bulging upper laminal cells associated with slightly thicker, flattened dorsal superficial walls, has not been emphasized by previous authors, but is common among the species examined, being present to various degrees in, e.g. W. artocosana (Pl. 59, f. 17), W. breutelii (Pl. 60, f. 5), W. canaliculata, W. condensa, W. controversa (Pl. 59, f. 7), W. ghatensis, W. glaziouii, W. latiuscula, W. ligulaefolia, W. macrospora, W. occidentalis, W. striata (Pl. 61, f. 19), W. termitidarum, W. triumphans, W. veviridis and W. wimmeriana.

            The best-developed species of Weissia, W. jamaicensis (Pl. 60, f. 16–20), includes a potpourri of features characteristic of other genera. It has the basal vee of hyaline cells of Tortella, the much-enlarged ventral stereid band and dilated leaf base of Pseudosymblepharis, and a peristome of 16 straight, linear-lanceolate teeth cleft to a basal membrane into two spiculose rami quite like that of Trichostomum crispulum (which, itself, occasionally develops a basal vee and margins incurved near the apex, but lacks the swollen ventral stereid band). In this case, the species are distinctive, but the generic definitions break down. Trichostomum crispulum and T. perligulatum have leaf margins that are often incurved near the apex but generally have plane or broadly incurved margins throughout most of the leaf. Some species, such as W. crispa (Pl. 60, f. 6–9) and the doubtfully distinct W. muhlenbergiana (Pl. 61, f. 1–6, see Crum & Anderson's 1981 discussion), have perichaetial leaves with plane to erect-incurved margins but cauline leaves (and those on sterile stems) with weakly but narrowly incurved upper margins, and are perhaps ultimately better assigned to Trichostomum in the T. crispulum relationship. Weissia rutilans (Pl. 61, f. 7–11) has upper laminal margins not easily assigned to either plane or narrowly incurved status. In any case, to provide an interim classification that better reflects perceived relationships, all Weissia taxa with clearly plane upper cauline leaf margins examined in the course of this study are here transferred to Trichostomum.

            The fact that peristome teeth may occasionally be represented in some species only by very much reduced, truncate and colorless fragments, these often hidden below the rim of the capsule mouth, indicates that past generic level distinctions between peristomate and gymnostomous species of Weissia with similar leaves may not be worthwhile. There is some correlation between thick capsule walls and lack of a peristome (reflected in distinctions between Weissia taxa of my treatments in the Moss Flora of Mexico, in press), but this must be investigated in greater detail. Stoneburner (1985) demonstrated significant variation in peristome expression in species of Weissia from the southwestern United States, and even found rudimentary teeth in a species (W. ligulaefolia) hitherto considered gymnostomous. She further discussed the “evanescent membrane” of hymenostomous species as a poor taxonomic character, explaining it as the upper surface of a somewhat persistent columella in both eperistomate and peristomate taxa. The present study confirms this in that a “hymenium” can often be seen below the peristome teeth of recently dehisced capsules of, for instance, W. controversa. This is an old problem. Referring to Brown's (1818) description of the then new genus Hymenostomum, Greville and Arnott (1824b) wrote: “In Dr. Hooker's excellent figure of Gymnostomum xanthocarpum in the Musci Exotici, the membrane which closes the sporular bag is admirably delineated.¼ It ought to be observed, that Palisot has described this membrane in the Mosses without a peristome, but denied it to the others” and (1824a) again asserted: “Now, every moss possesses this ‘membranula indivisa,' arising from the lining of the theca; but in all the species of Gymnostomum, it is peculiarly evident at some particular stage.” However, Greville and Arnott (1824b) admitted that: “The membrane to which we have already alluded, as closing the mouth of the sporular bag, there is every reason to suppose, is stronger and more durable in all such as have a naked peristome.”

            A further taxonomic complication is that the peristome teeth of occasional specimens, e.g. of W. triumphans, are somewhat twisted counterclockwise, possibly an indication of a relationship of these species to Tortella.

            Regarding the synonymy of Weissia and Astomum, a review of the problem and new evidence (existence of sporophytes of intermediate morphology) was offered by Stoneburner (1985). Many combinations at the genus level in Astomum and Hymenostomum remain as “correct” names in the list of species and infraspecies given at the end of this treatment. A mass transfer of these names to Weissia was considered but rejected because many names, on examination of authentic material, will prove to be more appropriately placed in Trichostomum (as emended here). Recognition here of subgenera of Weissia that are based largely on sporophyte morphology reflects recent studies by other authors (excepting subg. Phasconica). Quite probably, intraspecific lines of evolution involving sporophytic features of species with essentially identical gametophytes will be found that cut across presently recognized subgeneric limits. Unusual characters of sporophytes, such as the thick thecal walls of species of subg. Hymenostomum or the strongly bulging exothecial cells of W. macrospora, however, should also be evaluated and taken into account.

            A monotypic genus now in the Viridivelleraceae, Viridivellus Stone, may actually represent reduction of the Weissia gametophyte to an extreme, leaving only the stem and perichaetial leaves on a persistent protonema; Stone (1980b) indicated that this genus may be better placed in the Pottiaceae. It should be examined during future revisions of the genus Weissia.

     Brotherus (1924–25) placed Phasconica between Tetrapterum and Hymenostomum, among genera he felt intermediate between Astomum and Weissia. Hilpert (1933), who saw material of the generitype, Phasconia lorentzii, noted the closely inrolled upper laminal margins and suggested a relationship with Astomum. Crundwell and Nyholm (1972a, 1974) included Phasconica in Weissia subg. Astomum. Stone (1980b) carefully described and illustrated what is surely Phasconica balansae from Australia, showing the strongly incurved upper laminal margins characteristic of Weissia; however, she indicated a reluctance to follow Crundwell and Nyholm (1972a, 1974) in assigning the genus to Weissia subg. Astomum because of its macrostomous capsule with dehiscent flattened operculum, stout columella, and ventral surface of laminal cells distinctly mamillose and strongly papillose, among other characters. Magill (1981) suggested that because of similarities of gametophyte and dissimilarities of sporophyte (ex descr.) this genus “is reminiscent of the relationship between Weissia and the segregate genera Astomum Hampe and Hymenostomum R. Br.” Saito (1975, p. 417) reduced Phasconica to synonymy with Weissia, with no further explanation. Material of Phasconica C. Müll. s. str., seen during this study was found mixed in the type of Trachycarpidium verrucosum (P. tisserantii, PRE!, is referred to Trichostomum as a synonym of T. unguiculatum see Crundwell & Nyholm 1974), and the genus Phasconica is here given a new status as a subgenus of Weissia differing from other subgenera mainly by the macrostomous, eperistomate capsule with a short seta and a well differentiated, dehiscent operculum. Because of the unusual sporophyte morphology, subg. Phasconia may not be part of a reduction series in Weissia, but may instead be a remnant of a more primitive and now largely extinct lineage; further analysis should be done at the species level. Weissia platystegia (illustrated and discussed as Astomum platystegium by Eddy (1990) and Norris and Koponen (1989) belongs in subg. Phasconica.

            The singular Pseudosymblepharis socotrana, including the synonym Barbula (sect. Edentella) schweinfurthiana (isotype at BM) is transferred to Weissia (as W. artocosana, a nom. nov.) on account of the weakly papillose, ventrally bulging upper laminal cells, ventral stereid band smaller than the dorsal (Pl. 59, f. 17), and the lack of a peristome, all characters found in Weissia. The strongly sheathing leaf bases are found in both genera, and are variably demonstrated among species of Pseudosymblepharis. This species is gametophytically rather© similar to Rhamphidium but differs in the entire leaves and lack of a hydroid strand, as well as absence of a peristome.

            Hybrids have not only been reported between species of different subgenera of Weissia, but also between Weissia crispa and Tortella flavovirens (Nicholson 1910). The sporophytes in this last case apparently had short setae; the thecae were ovoid, partially cleistocarpous, rudimentarily peristomate, and covered by very large calyptrae (characteristic of Tortella flavovirens). The spores were also reported as remaining adherent in tetrads.    plus 11 in Astomum and 16 in Hymenostomum.

Literature: Anderson and Lemmon (1972, 1973, 1974), Andrews (1920, 1922a, 1924, 1933), Bryan (1956), Crundwell (1971b), Dietert (1979), Eckel (1986b), Flowers (1973b), Grout (1900), Khanna (1960, 1964), Lemmon (1968), Lewinski (1983), Mizushima (1957), Nicholson (1905a, 1906), Reese (1988, 1991), Reese and Lemmon (1965), Robinson (1966), Shaw (1987a), Stoneburner (1981, 1986), Stoneburner and Wyatt (1985), Williams (1966b), Zander (1985a), Zuttere et al. (1984).
Number of accepted species: 97
Species Examined: W. abbreviata (NY), W. andersoniana (BUF, TENN), W. argentinica (NY), W. artocosana (BM, NY), W. balansae (PC), W. balansaeana (MO), W. bizotii (PC), W. brachycarpa (BUF, NY), W. breutelii (BUF, NY), W. canaliculata (NY), W. condensa (BUF, TENN, NY), W. controversa, W. crispa (BUF, DUKE), W. diffidentia (US), W. edentula (MICH, NY), W. fallax (NY), W. felipponei (PC), W. ghatensis (BM), W. glaziouii (NY), W. jamesonii (TENN), W. jamaicensis (BUF, NY, TENN), W. latiuscula (BM), W. ligulaefolia (BUF, FH, NY), W. lineaefolia (NY), W. longidens (DUKE, NY), W. longifolia (NY), W. ludoviciana (DUKE), W. macrospora (NY), W. muhlenbergianum (DUKE), W. newcomeri (FH), W. occidentalis (COLO), W. opaca (NY), W. ovalis (NY), W. platystegia (BM), W. riograndensis (H), W. rutilans (BUF, NY), W. semidiaphana (BUF, FH), W. sharpii (BUF, DUKE), W. subacaulis (NY), W. submicacea (NY), W. termitidarum (NY), W. triumphans (NY), W. unguiculata (NY), W. veviridis (H), W. wimmeriana (NY).


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            Plants in low cushions or turfs or loosely caespitose, green above, brown to tan or yellow below. Stems branching irregularly, to 1.0 cm in length, transverse section rounded-pentagonal, central strand present, occasionally hollow or very thick, sclerodermis weakly differentiated in 1–2 layers, hyalodermis weakly differentiated to distinct, seldom absent; axillary hairs to 10 cells in length, basal 1–2 cells thicker walled; sparsely radiculose. Leaves incurved, tubulose, often contorted or spiralled when dry, spreading and occasionally sharply reflexed above a sheathing base when moist, long-ligulate, oblong or triangular to lanceolate, 1.5–2.5(–4.0) mm in length, upper lamina broadly channeled across leaf, seldom narrowly channeled along costa, margins sharply incurved (or occasionally tightly involute) above the leaf base, seldom merely erect-incurved near apex, entire, occasionally fragile and breaking off in large rectangles; apex sharply acute to subulate, occasionally broadly acute, obtuse, or weakly cucullate; base scarcely differentiated to ovate or rectangular, occasionally half-sheathing; costa shortly and sharply mucronate, seldom subpercurrent, superficial cells quadrate or occasionally short-rectangular to elongate ventrally, elongate dorsally, 4–8(–10) rows of cells across costa ventrally at midleaf, costal transverse section ovate, occasionally circular or semicircular, two stereid bands present, usually of about equal size, differentiated epidermis present ventrally, absent or occasionally weakly differentiated dorsally, guide cells 4–6(–8) in 1 layer, hydroid strand absent or occasionally present; upper laminal cells subquadrate to hexagonal, 7–13 µm in width, 1:1, walls thin to evenly thickened, superficially strongly bulging on both exposed surfaces or more strongly protuberant on ventral surface; papillae bifid, 2–6 per lumen, occasionally fused into a capitulate papilla covering the lumen, occasionally spiculose-branching, seldom absent; basal cells differentiated across leaf, occasionally rising higher along margins in a vee, rectangular, occasionally rhomboidal, 2–5:1, walls thin to evenly thickened. Rhizoid-borne tuber-like propagula reported for W. controversa. Monoicous, occasionally dioicous. Perichaetia terminal, inner leaves little different from cauline leaves or somewhat larger, occasionally weakly sheathing the seta, lower cells long-rhomboidal to midleaf. Perigonia appearing as stalked lateral buds on perichaetiate plants (but variably present) or terminal on usually smaller perigoniate plants. Seta 0.1–1.3 cm in length, 1(–2) per perichaetium, yellowish brown, twisted clockwise; theca 1.0–2.2 mm in length, occasionally inclined, yellowish to reddish brown, elliptical to ovate or cylindrical, occasionally nearly spherical or urceolate, exothecial cells rectangular, walls thin or becoming rather thick, rarely superficially bulging, stomates phaneropore at base of capsule, annulus of 2–6 rows of persistent, vesiculose cells, often on a differentiated collar, or annulus not differentiated; cleistocarpous or stegocarpous, peristome teeth 16, short or rudimentary or absent, occasionally lifts with operculum, oblong-truncate to long-triangular, often irregularly cleft into two rami or variously perforate, papillose to spiculose or spirally ridged, to 125(–250) µm, with up to 10 articulations, straight or twisted weakly counterclockwise, basal membrane absent or low, low-spiculose, mouth of capsule occasionally closed by a hymenium, this internal to the peristome (when peristome present), seldom macrostomous. Operculum conic to rostrate, 0.3–0.8(–1.5) mm in length, cells straight or rarely somewhat twisted counterclockwise.

Calyptra cucullate (to short-triangular on cleistocarpous capsules), smooth, 0.4–2.5 mm in length. Spores 14–28 µm in diameter, brown to yellowish brown, low-papillose or occasionally highly papillose. Laminal KOH color reaction yellow, usually pale yellow. Reported chromosome number n = 13, 13+m, 13+0–4m, 14, 26 (subg. Weissia); 13, 13+m, 26 (subg. Astomum); 8, 13, 14, 26 (subg. Hymenostomum).

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