Trematodon, MICHX.

Belkina, Olga A. & Vilnet, Anna A., 2019, Trematodon laetevirens Hakelier & J. - P. Frahm and T. brevicollis Hornsch. (Bruchiaceae, Bryophyta) in Russia, Cryptogamie, Bryologie 20 (19), pp. 247-258 : 254

KEY TO RUSSIAN SPECIES OF TREMATODON MICHX.

1. Costa in cross section with stereids; capsule neck strumose on most of mature sporophytes; neck equal of urn or much longer ............................................................................................................................................ 2

— Costa in cross section without stereids; capsule neck not strumose on mature sporophytes; length of neck almost equal of urn or, in Far East, sometimes longer ............................................................................................. 3

2. Capsule neck about 1.3 time the length of urn or much longer; costa not filling the entire width of the linearsubulate acumen; leaf more or less gradually narrowed to upper part; leaf margins bistratose in subula .......... ........................................................................................................................................ T. longicollis Michx.

— Capsule neck about the length of urn; costa filling the entire width of the subula; leaf from obovate or oblong base suddenly narrowed to long subula ........................................................... T. ambiguus (Hedw.) Hornsch.

3. The largest perichaetial leaf straight, oblong or spathulate, rounded on the apex or with very short obtuse apiculus; capsule straight, erect on most plants; transition of the neck to the seta gradual and difficult to discern; exothecial cells rectangular to quadrate, with slightly thickened walls; peristome teeth perforated along tooth length and split above; on sterile plants stem leaves from obovate or elongate-obovate base gradually narrowed to long upper part. ................................................................................ T. laetevirens Hakelier & J.-P. Frahm

— Largest perichaetial leaf with acute more or less long apiculus; capsule mostly incurved, more or less inclined; transition of the neck to seta gradual, but clearly visible; exothecial cells narrow, thick walled; peristome teeth usually whole, blunt; on sterile plants stem leaves suddenly or more gradually narrowed to long upper part ... .................................................................................................................................... T. brevicollis Hornsch.