Meesiaceae. Genus Meesia

1. Leaf margins plane 2

Leaf margins recurved 3

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 (35(8) cm vs. 510 cm) of M. hexasticha is helpful in distinguishing it from M. longiseta in the field.

Costae 1/22/3 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.