高加索铁角蕨 gao jia suo tie jiao jue

Asplenium septentrionale (Linnaeus) Hoffmann subsp. caucasicum Fraser-Jenkins & Lovis, Notes Roy. Bot. Gard. Edinburgh 38: 281. 1980.

Plants 8-15 cm tall. Rhizome shortly creeping to ascending, apex scaly; scales dark brown, narrowly triangular to subulate, entire to denticulate, at base fimbriate. Fronds caespitose; stipe shiny castaneous only at base, abruptly green toward rachis, 6-10 cm, 2-3 × as long as lamina, with unicellular glands or subglabrous, apex 2- or 3-forked; segments linear, 2-3 × 0.1-0.15 cm, base gradually decurrent onto stipe, minutely forked again at apex. Fronds without distinct rachis, green, other veins slender and subparallel to central axis, 1 veinlet per ultimate segment. Fronds herbaceous-leathery, grass-green. Sori 1-5 per segment, linear, 1-2 cm, on acroscopic veins and close to costa, at maturity covering entire surface; indusia brown, linear, membranous, free margin often with unicellular glands, entire-sinuate, opening toward main vein (costa), persistent but reflexed and covered by sporangia at maturity. Spores with lophate perispore, average exospore length 32-36 µm. Plants sexual diploid: 2n = 72.

In crevices of non-calcareous (often granitic) rocks in open or partial shade; below 4100 m. ?Taiwan, Xinjiang, Xizang [Afghanistan, N India, Pakistan, Russia; SW Asia (Abkhazia/Georgia, Azerbaijan, Iran, Turkey), E Europe].

Asplenium caucasicum is the diploid ancestor of the more common autotetraploid A. septentrionale (see below). This taxon is best known from the Caucasus region, but microcharacters have shown its presence in Xinjiang. A recent chromosome count from Xizang confirms its presence in China. A doubling of its genome has led to the origin of autotetraploid A. septentrionale. In places where both taxa grow together, their triploid sterile hybrid, A. ×dirense Viane & Reichstein, can be expected.

Asplenium sasakii (Hayata) Makino & Nemoto was distinguished from A. septentrionale by its narrower fronds (a.o., Tagawa, Acta Phytotax. Geobot. 10: 204-205. 1941); it may be an earlier name for A. caucasicum if Taiwanese plants turn out to be diploid. However, at present, no chromosome counts or flow-cytometric data are available for Taiwanese plants.