Rhynchostegium serrulatum
Rhynchostegium
leaves erect-spreading or erectopatent, ovate-lanceolate, often twisted mid leaf, 1.3–2 × 0.6–0.8 mm;
margins serrulate to serrate;
apex gradually acuminate;
costa to 40–70% leaf length, terminal abaxial spine absent;
alar cells undifferentiated, or 1–4 cells slightly differentiated, or, rarely, slightly larger cells forming indistinctly differentiated group not reaching margins;
laminal cells (50–)80–120(–160) × 7–9(–10) µm;
basal cells short-rectangular, region in 1–2(–3) rows, indistinctly differentiated or sometimes forming conspicuous pellucid belt across base.
leaves erectopatent or erect, gradually reflexed from erect base, imbricate to somewhat spaced, broadly ovate or suborbicular to ovate-lanceolate, flat to slightly concave, not or slightly plicate;
base with decurrency absent after leaf is detached;
margins serrate to serrulate;
apex acuminate or ± broadly acute;
costa to 40–85% leaf length, moderate to somewhat stout, terminal abaxial spine present or absent;
alar cells poorly differentiated, or short-rectangular, slightly enlarged, region inconspicuous;
laminal cells linear, walls moderately thick;
basal cells somewhat shorter.
similar, smaller, sometimes narrower.
2–3 cm.
red-brown, smooth.
autoicous;
perichaetial leaves abruptly contracted, acumen straight to reflexed.
1.7–2 mm;
operculum narrowly long-rostrate.
inclined to horizontal, red-brown to brown, oblong-cylindric, weakly curved;
annulus separating;
operculum rostrate;
peristome xerocastique, perfect.
naked.
9–11 µm.
9–16 µm.
Rhynchostegium serrulatum
Rhynchostegium
Rhynchostegium serrulatum can be recognized in the field by its light green color and somewhat complanate foliage. The long leaves with long laminal cells allow rather easy separation from Oxyrrhynchium hians. Sterile collections are sometimes confused with Sciuro-hypnum curtum, but that species usually has conspicuous groups of enlarged alar cells; in R. serrulatum laminal cells are rather homogeneous across the whole base as they are somewhat enlarged and have a specific appearance rather characteristic for this genus. This pattern of leaf base areolation distinguishes R. serrulatum from Brachythecium asperrimum, which is sometimes superficially similar; this Pacific coast species has a small but rather well-differentiated alar group of pellucid cells. In addition, the axillary hairs of R. serrulatum are 3–5-celled, often brownish, while in B. asperrimum they are 2- or 3-celled, short, and pellucid. Rhynchostegium scariosum (Taylor) A. Jaeger from Mexico differs mainly due to its small plants with stem leaves 0.9–1.3 mm; it might be expected in the southeastern United States.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Species 30–60 (2 in the flora).
Aquatic plants of Rhynchostegium were often segregated as the separate genus Platyhypnidium, placed in Amblystegiaceae by M. Fleischer (1900–1922[–1923], vol. 4) and V. F. Brotherus (1924–1925). The latter genus was subsequently accepted by many bryologists, although some authors (such as J. Podpěra 1954; N. Takaki 1956; H. Robinson 1962) included it in Rhynchostegium. Phylogenetic analyses by S. Huttunen and M. S. Ignatov (2010) found that aquatic species within Rhynchostegium originated several times, thus the acceptance here of Rhynchostegium in a broad sense. Robinson (1987) recognized the tropical species as distinct from the European R. confertum (Dickson) Schimper, the type species of the genus, and he segregated tropical taxa into Steerecleus. However, the broader analysis by Huttunen and Ignatov demonstrated that species with Steerecleus morphology are not monophyletic, so acceptance of this genus would cause severe splitting of Rhynchostegium and enormous nomenclatural problems. The North American species represent quite morphologically different lineages, Steerecleus and Platyhypnidium.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Plants terrestrial; leaf apices gradually acuminate. | R. serrulatum |
1. Plants aquatic; leaf apices ± broadly acute. | R. aquaticum |
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