16. Dryopteris caucasica (A. Braun) Fraser-Jenk. & Corley (Brit. Fern Gaz. 10: 221-231. 1972).—Fig. 17.

Rhizome usually ascendent at apex, horizontal below, stout, forming offshoots. Fronds to 105 cm, erect, spreading, fasciculate; stipe 1/4-1/2 length of blade, the scales sparse, pale brown, narrowly triangular to ovate-lanceolate, up to ca. 2 cm long, toothed towards the attenuate apex; blade to ca. 80 cm long, 35 cm wide, mostly ovate-lanceolate to elliptic, flat, herbaceous, 2-pinnate; pinnae to 20 cm long, 5 cm wide, lanceolate or frequently narrow long triangular with attenuate apex, pinnatisect to pinnate, the pinnules (or segments) with margins entire to mostly lobed, the lobes with very acute, distinct teeth usually arranged in pairs. Indusia very thin, membranous, white, greatly overlapping the sporangia shortly before maturity, edges lacerate, rapidly shrivelling.

Dryopteris caucasica is a diploid, sexual species native to forests in the alpine regions of the Middle East (200-800 m elev.). It was introduced into U.S. cultivation very recently, probably from horticultural sources in Britain originating from Fraser-Jenkins’ collections. Dryopteris caucasica is one of the parent species of D. filix-mas and is best distinguished from it by the generally paler color of the lamina, the doubly-toothed margins of the segments, and the indusia which are white at all stages (until shrivelling) and have lacerate margins. The distinct acuteness of the usually paired teeth at the apex of the pinnules (or segments) and their lobes, and the flatness, thinness and lacerate margin of the indusia are the main characters of this fern. In case of doubt, its very dark spores distinguish it from D. filix-mas. Wild plants apparently do not form side crowns as readily as those in cultivation.

Dryopteris caucasica is easily cultivated, and is deciduous at first frost. It is hardy to at least 30°F and perhaps to 20° F, but doesn’t tolerate summer drought as well as D. filix-mas.