Andreaea schofieldiana and A. megistospora, species novae, and Taxonomic Criteria for Sect. Nerviae (Andreaeopsida)

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Abstract
Andreaea schofieldiana, known from British Columbia (type) [Canada] and California [USA] differs from its closest relative, the European endemic species A. frigida Hub., by its smaller size, smaller spores (20-30[36] .mu.m), membranous leaf texture, strongly biconvex costa, the occasional presence of low papillae on its perichaetial bracts, and its occurrence in dry, exposed habitats. Andreacea megistospora is most closely related to A. rothii Web. and Mohr. from which it differs primarily by its very large spores, about 50-100 .mu.m, the largest in the genus. The subspecies megistospora, with the lamina distinct throughout the leaf and papillose inner perichaetial bracts, is disjunct between northwestern parts of North America and Europe. In Alaska, British Columbia, and Washington, it is the most common member of section Nerviae Card. ex. Broth.; in the British Isles (type: Scotland) and Norway, it is quite rate. The subspecies epapillosa, with the lamina indistinct in the subula and epapillose perichaetial bracts, is occasional in southeastern Alaska and coastal British Columbia (type) and is often found growing with ssp. megistospora. Spore size is considered the major criterion for defining taxa in section Nerviae. Stress on spore size, rather than on traditional leaf characters that vary within species, led to a realignment of taxa in section Nerviae, which have long been confused. A key to costate Andreaeae of North America and Europe is provided.

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