Leaf thickness variation and leaf cross-sections of specimens from the different geographic areas.

(a) Orthotrichum shevockii from western North America; (b) samples from Tenerife, (c) O. kellmanii from California. (a,b) from left to right: bistratose leaf (except base), leaf with a bistratose upper part and bistratose bands, leaf with dispersed bistratose bands in the upper part, leaf almost unistratose with bistratose patches around the apex. (c) top: bistratose leaf (except base), bottom: leaf with bistratose upper part and bistratose bands. Each leaf belongs to a separate individual. Cross-sections belong to a different leaf of the same individual. Arrowheads indicate bistratose strands or margins; in (c) they indicate the tristratose margins. Scale bars: leaves = 0.5 mm, cross sections = 100 μm. Vouchers: a, Shevock & Anderson 16754 (UC 1754230), Lara, et al. s.n. (MAUAM-Brio 3289), Shevock & York 13404 (CAS 958716, paratype of O. shevockii), Shevock 21802 (UC 1754431); b, J.M.B., J.G.M. & J.L.P s.n., (TFC-Bry 15957), Losada-Lima s.n. (TFCBry-17428), Losada-Lima, León & Díaz s.n. (TFC-Bry 15861), Losada-Lima, León & Díaz s.n. (TFC-Bry 15904); c, Shevock 32935 (NY 1140598).