THE GENUS BRYUM (BRYACEAE, MUSCI) IN MIDDLE ... - Arctoa

162
V. I. ZOLOTOV
31 32
33 34 35
Figs. 31-35. Exostome tooth border: inner surface (31), outer surface (32), and transition zone of tooth, outer
surface (33-35). 31 – B. caespiticium Hedw. (Moscow Prov., Pushchino, Ignatov, 18.VI.1996, MHA, 3400x); 32
– B. wrigtii Sull. et Lesq. (Chukotka, Afonina: Bryophyta Rossica et Civ. Coll Near. Exs., 54, MW, 1740x); 33 –
B. arcticum (R. Br.) B. S. G. (Komi Republic, Ukhta [Archangelsk Prov.], Zickendrath 3.VII.1895, H, 1450x); 34 –
B. capillare Hedw. (Switzerland, K. Korotkov, 1992, MW, 2230x); 35 – B. wrigtii (Chukotka, Afonina: Bryophyta
Rossica et Civ. Coll Near. Exs., 54, MW, 2100x).
related species (Fig. 55).
Lower and middle portions of the exostome
teeth have a border. This zone is 4-12 mkm wide
and appears pellucid under the light microscope.
Under SEM, it is defined as a marginal area that
is: (1) much thinner than the central part of the
plate; and (2) lackingthe ornamentation developed
in the central part of the plate. The tooth
border often is considered as being composed
only from the OPL, without PPL material; however,
at least at the inner trabeculae, the PPL contributes
some material to its formation (Figs. 31-
32). The width of the tooth border is a useful
character for some sections of the genus; for example,
species with a + reduced peristome (B.
knowltonii, B. arcticum) usually have a narrower
border. The tooth border also is relatively narrow
in species of the B. erythrocarpum complex.
The endostome of Bryum has a more variable
structure than the exostome. The most highly developed,
or perfect, endostome hasa high basal membrane
(about 1/2 the endostome length), broad
segments, and 2-3(-4) cilia with long appendiculae.
In this case, the endostome leaves only a small