2. Leaves
distinctly tristichous, more or less appressed at base, reflexed to
horizontal above, strongly keeled; margins serrate; plants
dioicous 1. M. triquetra
A widespread species in some
Arctic regions. Rare in the boreal zone where it occurs in rich
fens mixed with other rare and rapidly declining species such as
Paludella squarrosa, Cinclidium stygium, Hamatocaulis vernicosus,
Scorpidium revolvens, and Drepanocladus trifarius. Conspicuously trifarious leaves make this species immediately
recognizable.
— Leaves not in apparent
rows, erect-spreading, weakly keeled; margins entire or slightly
serrulate near apices; plants autoicous 2. M. longiseta
Meesia longiseta is
known from many Arctic and boreal regions of Russia, but most
Russian records date from the 19th and early 20th centuries, while
21th centure collections are known only from Urals. Its rapid rate
of decline makes M. longiseta one of the most critically
endangered rich fen species. However, it remains only moderately
rare in Chukotka where it occurs in fens, wet tundras, swampy lake
shores, and open Larix forests. Collections of M. longiseta commonly have sporophytes and the presence of very
long setae in combination with distinctly curved capsules greatly
help in recognizing the species.
3. Costae
1/5 width of leaf base; deoperculate capsules inclined to
horizontal, curved, mouth facing somewhat downwards to horizontal
3. M. hexasticha
This is a rare species in
Yakutia, Chukotka, and the Kola Peninsula (where it was only
recently found). The leaves of M. hexasticha are rather
similar in shape to those of M. longiseta, but they have
recurved margins (in contrast the leaf margins of M. longiseta
are plane). In addition the shorter setae (3–5(–8) cm vs. 5–10 cm) of M. hexasticha is helpful in distinguishing it
from M. longiseta in the field.
— Costae 1/2–2/3 width of
leaf base; deoperculate capsules erect below, slightly curved above,
mouth facing upwards to horizontal 4. M. uliginosa
Messia uliginosa has
the widest distribution in Russia of any species of the genus. It is
a northern and mountain species often found in calcium-rich mires,
associated with other rich fen species. It also is found on wet rock
outcrops and cliffs near waterfalls. Populations of M. uliginosa
appear to be fairly stable, although the species has disappeared
from some boreal regions, e.g., the species is known from the
Moscow Province only by a single collection made in 1890.