Symbiezidium

  • Authority

    Gradstein, S. Robbert. 1994. Lejeuneaceae: Ptychantheae, Brachiolejeuneae. Fl. Neotrop. Monogr. 62: 216. (Published by NYBG Press)

  • Family

    Lejeuneaceae

  • Scientific Name

    Symbiezidium

  • Type

    Lectotype (Evans, 1907a). Symbiezidium transversale (Swartz) Trevisan.

  • Synonyms

    Platylejeunea, Symbiezidium transversale (Sw.) Trevis., Lejeunea taeniopsis Spruce, Symbiezidium transversale var. hookerianum (Gottsche) Gradst. & J.Beek

  • Description

    Genus Description - Plants usually large, up to 15 cm long × 2-5 mm wide, green to brown when alive, usually becoming somewhat darker in the dried condition, creeping to pendent. Branching sparse to irregularly pinnate, vegetative branches of the Lejeunea type or Frullania-type, short sexual branches of the Lejeunea-type, flagelliform branches lacking. Stems rigid, 0.15-0.3 mm in diam., epidermal cells rectangular, 2-3× broader and 1-1.2× higher than the medullary cells, dorsal epidermal cells as large as or slightly larger than ventral epidermal cells, all cell walls colorless and thickened, the outer epidermal wall ± evenly thickened, the inner cell walls with large, confluent trigones; ventral merophyte 4-8 cell rows wide. Leaves widely spreading, convex, little altered when dry, ovate-oblong to ligulate, at opposite sides of the stem often different in length, apex rounded to apiculate, sometimes recurved, margins entire or, rarely, toothed near apex (Symbiezidium dentatum), dorsal base usually auriculate, extending ± across the stem and attached to the stem by 2 or 4 (!) U-shaped cells (cross-section), ventral margin straight or concave, the keel very short and curved, making a wide angle with the ventral margin; leaf cells isodiametric-hexagonal, averaging 30-40 m, with triradiate trigones and one intermediate thickening on longer walls; oil bodies Bazzania-type; ocelli lacking. Lobules small, l/10-l/4× leaf length, never reduced, hidden behind underleaves, strongly inflated and sac-like, free margin incurved, ± flattened towards apex, apex with a one-celled tooth or notched, hyaline papilla hidden on inner surface of the lobule proximal of the apex. Underleaves imbricate, large, (3-)4-10× stem width, apex rounded or truncate, margins entire, bases widely rounded, decurrent and with deeply arched insertion line, tristratose in cross section (insertion line shallowly curved and base bistratose in the African subgenus Eosymbiezidium), with 4-8 superior central cells; brown, adhesive rhizoid discs, consisting of coalesced, thick-walled rhizoids, produced in epiphyllous plants. Androecia on short-specialized or elongated branches, bracts much smaller than leaves, subequally bilobed, lobule hypostatic, underleaves limited to the base of the male spike; antheridia two per bract. Gynoecia on very short Lejeunea-type branches, hidden behind stem leaves, usually with one short pycnolejeuneoid innovation, occasionally innovation lacking; bracts in one series, suberect, much smaller than vegetative leaves, subequally bifid, apex of lobe and lobule rounded, keel long, rounded, without wing; bracteoles longer than underleaves, apex rounded or short bifid. Perianths small, subcylindrical, usually shorter than vegetative leaves, flattened, the ventral surface usually slightly inflated, with sharp lateral keels and 0-2 small ventral plicae, lateral keels ciliate-laciniate in the upper half, sometimes the keels almost smooth, ventral surface smooth or roughened by ciliae or laciniae, dorsal surface smooth (perianths entirely smooth in Eosymbiezidium). Sporophyte: seta articulate; spores with a complex ornamentation consisting of clustered verrucae and baculae, and rosettes (van Slageren, 1985: 269); otherwise as in the tribe. Vegetative reproduction not observed.

  • Discussion

    Symbiezidium is a very well defined genus. Recent authors considered it an autonomous genus complex (Gradstein & van Beek, 1985) but in this treatment Symbiezidium is classified as the most primitive member of the Brachiolejeuninae. With other members of this subtribe it shares the presence of an enlarged epidermis, the large leaf cells with radiate trigones, the lack of ocelli, the flattened, ciliate perianths and the tristratose underleaf bases. Symbiezidium differs from all other genera of the Brachiolejeuninae by its specialized male spikes with reduced underleaves, its abbreviated gynoecial branches and by the innovations which are single and short, sterile or male, or are sometimes lacking. All of these characters are shared with Stictolejeunea. It would thus appear that Symbiezidium bears some affinity to members of the subtribe Stictolejeuninae and links the Brachiolejeuneae to that subtribe.

    The neotropical species of Symbiezidium are recognized by their elongated, oblong leaves, the large underleaves (5-10× stem width) with deeply arched insertions, and the small, strongly inflated pouched lobules with incurved free margin, which are hidden behind the underleaves and ± devoid of teeth. In Marchesinia brachiata, which resembles Symbiezidium when sterile, the lobules are rather flat and distinctly toothed along the free margin (except when reduced). When fertile, Symbiezidium stands out by its almost sessile, ciliate-laciniate perianths, inserted on a very short branch and partially or entirely hidden behind the vegetative leaves. In some populations of S. transversale var. transversale, however, perianth keels may be almost smooth (e.g. Nicaragua, Proctor et al. 27220). Except for S. dentatum, the neotropical species of Symbiezidium are difficult to identify when mature perianths are lacking.

    Distribution and Ecology : Symbiezidium is an Afro-American genus with three species in the neotropics and one species, S. madagascariense, on Madagascar and the Seychelles. The latter species differs considerably from the neotropical species and has been placed in a separate subgenus Eosymbiezidium by Gradstein and van Beek (1985). In tropical America, species of Symbiezidium are very common epiphytes in virgin or degraded rain forests at rather low elevations. In more mesic areas, such as the Galapagos Islands (Gradstein & Weber, 1982), the genus is usually lacking