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Published In: Muscologia Recentiorum 4: 78. 1819[1818]. (Muscol. Recent.) Name publication detail
 

Project Name Data (Last Modified On 2/17/2011)
Acceptance : Accepted
Project data     (Last Modified On 2/17/2011)
Discussion:

Racomitrium is usually recognized by its strongly sinuose leaf cells. There are some Grimmia species with sinuose lower leaf cells and these may be difficult to distinguish from depauperate collections of Racomitrium without examining stem cross‑sections: Racomitrium lacks a central strand, nearly all Grimmia species have one. The leaf apices in Central America collections of Racomitrium are especially variable. In both species some collections are fully muticous, others always have long, hyaline tipped leaves, while still others have both types of leaves.

The Racomitrium peristome has a basal membrane and variably 2–3-cleft teeth. In some species the teeth are filiform and rarely united by trabeculae. In others they are weakly cleft and have well-developed trabeculae that hold the divisions together. The peristomes with free, filiform divisions approach those of Ptychomitrium, while the weakly cleft teeth are similar to strongly cribrose Grimmia peristomes. The peristomial basal membrane in Racomitrium is often obscured by a prostome that occasionally exhibits a cell pattern indicative of an OPL or exostomial origin. Although peristome and calyptra form are important in assessing generic relationships within the Grimmiaceae, characters from these structures do not correlate in Racomitrium: peristomial evidence places it between Coscinodon and Ptychomitrium, while calyptral evidence places it between Coscinodon and Grimmia.

Racomitrium languginosum (Hedw.) Brid. was recently collected in Costa Rica (San José: Holz & Schäfer-Verwimp CR99-1212, GOET, MO). It is distinguished from other Central American Racomitrium species by its leaves that have long, erose-dentate, conspicuously decurrent hairpoints.


 

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Racomitrium Brid., Muscol. Recent. Suppl. 78. 1819. 

Plants robust in olive‑green, yellowish green, at times hoary tufts or mats. Stems erect, sparsely branched or with numerous fasciculate branches, central strand absent. Leaves erect‑spreading, homomallous or falcate, ovate‑lanceolate, strongly or weakly decurrent; apices acute to acuminate, hyaline‑tipped or muticous and rounded; margins uni‑ or bistratose, entire; costa strong, subpercurrent, percurrent or excurrent; cells smooth or papillose, with thick, strongly nodulose walls; upper cells usually short, basal cells elongate, alar cells often differentiated, smooth. Dioicous. Seta single or multiple, straight, twisted (clockwise or counter clockwise) when dry. Capsules exserted, erect, symmetric; stomata in neck; opercula erect‑subulate; annuli or 3–4 rows of cells; peristome of 16 teeth united at base, divided above in 2–3 linear, papillose divisions. Calyptrae large, mitrate, non‑plicate.

 

 

 
 
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