MIelichhoferiaceae. Genus Mielichhoferia

1. Stems in cross section distinctly pentagonal, central strands well or poorly developed; leaves narrowly triangular, not or only slightly narrowed to the insertions; leaf cells thick-walled 1. M. mielichhoferiana

Mielichhoferia mielichhoferiana is known in Russia from the Caucasus (Dagestan, North Ossetia, Karachay-Cherkessian Republic, Krasnodar Territory), southern Taimyr, Yakutia (Mus-Khaya Mt. area), Magadan Province, Chu­kotka, and Kamchatka (Klyuchevskaya Sopka Volcano). In the Caucasus it is considerably more common than M. elongata, which has been found only once in that region. It is the only species of the genus in Kamchatka. In Yakutia (Mus-Khaya Mt. area) Mielichhoferia is especially abundant due to the high heavy metal content in the rocks, and in this area M. mielichhoferian, M. asiatica and M. elongata have been found growing together. In other areas M. mielichhoferiana grows on shists and volcanic rocks often in moist places near waterfalls and along creeks. Critical identification features of M. mielichhoferiana include stems that in cross section are distinctly pentagonal and have large central strands. Previous to the revision of the genus in Russia (Tubanova et al., 2017) M. mielichhoferiana was thought to be the only species of Mielichhoferia in Russia.

— Stems in cross section round or indistinctly pentagonal, central strands weakly developed; leaves narrowly ovate, narrowed to the insertions; leaf cells thin- or firm-walled 2

2. Leaf marginal teeth sharp, straight to reflexed; upper leaf cells prorate; peristome elements less than 100 mm, smooth to lightly papillose 4. M. japonica

This species is known in Russia only from the southern Kuril Islands (Kunashir and Iturup) on the slopes of old volcanoes between 700 to 1300 m elev. It grows on acid volcanic rocks; in Kunashir it was collected in a mountain slope cave, while in Iturup it grew on rocks in the bed of a temporary brook. Superficially it looks like a small M. elongata, but differs in having leaves with long, narrow cells and regularly reflexed marginal teeth. Collections with mature capsules can be recognized by their strongly reduced peristomes (ca. 50 mm long). At times the peristomes appear to be absent because they hardly project above the large, decidous annuli. In contrast, other Russian Mielichhoferia species have longer (150–450 mm long) peristomes.

— Leaf marginal teeth somewhat sharp or blunt, not reflexed or a few teeth near leaf apices reflexed; leaf cells smooth throughout or sometimes subapical cells prorate; peristome elements more than 250 mm, more or less papillose 3

3. Leaves (0.4–)0.6–1.00.25–0.38 mm; leaf margins finely serrulate to subentire, marginal teeth not reflexed; leaf cells thin-walled; rhizoids pale, smooth to finely granulose 2. M. elongata

In Russia, unlike North America, M. elongata is a rarer species than M. mielichhoferiana. Ithas been found once in the Caucasus (in Kabardino-Balkarian Republic where other species of the genus are absent); it is also known from a single locality in southern Taimyr, several places in Yakutia, one locality in Zabaikalsky Territory and one locality in Chukotka. Mielichhoferia asiatica is very close to M. elongata and par­ti­ally replaces it in Yakutia and Transbaikalia. Mielich­ho­feria elongata grows on wet rocks (ultrabasites and schists) rich in heavy metals. It is distinguished from M. mielichhoferiana by the presence of round or round-elliptical stem cross-sections and leaves that have weakly serrulate margins and thin-walled cells. For differences between M. elongata and M. asiatica or M. japonica see discussions under those species.

— Leaves 0.4–0.70.18–0.25(–0.3) mm; leaf margins serrulate, uppermost marginal teeth short and often reflexed; leaf cells firm-walled; rhizoids brownish to reddish, coarsely papillose 3. M. asiatica

Mielichhoferia asiatica is mostly restricted to East Siberia (Yakutia, Irkutsk Province, Zabaikalsky Territory and Buryatia); it is also known from Sakhalin Island in the Russian Far East. As with other species of the genus it grows on rock outcrops and cliffs along creeks and streams, often in crevices and on overhanging surfaces where it forms extensive, low tufts. It differs from M. elongata in having smaller leaves, 0.4–0.70.18–0.25(–0.3) vs. (0.4–)0.6–1.00.25–0.38 mm; teeth on the upper leaf margins sharp, often recurved at 90° vs. blunt, subentire to slightly serrulate; firm-walled vs. thin-walled leaf cells; and coarsely vs. finely papillose rhizoids. It is also similar to M. mielichhoferiana in having firm-walled leaf cells and short, but sharp teeth on the leaf margins; however, leaves of M. asiatica are smaller, 0.4–0.7 vs. 0.6–1.0(–1.5) mm long than those of M. mielichhoferiana, and they are distinctly narrowed to the insertions while M. mielichhoferiana leaves are widest at the insertions. In addition; the two species have different stem transverse sections: M. asiatica, round-elliptical (rarely indistinctly pentagonal) with weak central strands; M. mielichhoferiana, sharply pentagonal with well-developed central strands. Mielichhoferia japonica differs from M. asiatica in having longer teeth on the leaf margins and longer leaf cells; furthermore, its peristome is vestigal, scarcely exceeding annulus, whereas in M. asiatica the exostome teeth are ca. 450 mm long.