Aneura mirabilis

Aneura mirabilis is a subterranean myco-heterotroph that obtains its nutrients from the abundant fungi growing among its tissues rather than from photosynthesis. The infecting fungus is a basidiomycete, a species of Tulasnella, which is also the case in fungi associated with other species of Aneura,^[5] as well as the related genus Riccardia. However, this is not the case for other members of the Metzgeriales that have been studied.^[3] Plants are white, lacking chlorophyll, and their plastids do not differentiate into chloroplasts.^[4] They are small, seldom growing more than 3 cm (1.2 in) long.^[6]

The species is dioicous, with individual plants producing either antheridia or archegonia, but never both. The female plants (with archegonia) are typically ten times the size of the male plants.^[3] The development of reproductive structures is not controlled by photoperiod, but does require a temperature of at least 21 °C (70 °F) following a period of sufficiently low temperature.^[7]

Aneura mirabilis was first reported by M. Denis in 1919, who considered it simply as a form of A. pinguis lacking chlorophyll.^[5] In 1933, S. Malmborg placed it in a separate genus, Cryptothallus. Apart from lacking chlorophyll, it is very similar to species in the genus Aneura, and the validity of recognizing Cryptothallus as a separate genus was questioned by Karen Renzaglia in 1982, who suggested it may be considered "merely as an achlorophyllous species of Aneura."^[8] A molecular phylogenetic study in 2008 placed the species firmly within Aneura, and it was transferred to that genus.^[5] This decision was confirmed by a larger molecular phylogenetic study in 2010.^[9]

It is suggested that the ancestor of Aneura mirabilis, like the related A. pinguis, had a mutualistic mycorrhizal association with Tulasnella, which was also able to form mycorrhizal connections with neighbouring trees. This evolved into a relationship where A. mirabilis gave up photosynthesis and obtained all its nutrients from the fungus, which in turn obtained them from the associated trees. Other evolutionary lineages of myco-heterotrophic plants have been shown to have evolved from photosynthetic, mycorrhizal ancestors.^[5]

Initially, A. mirabilis was the only species of bryophyte known with the same combination of characteristics,^[10] but in 1977 and 1979, a second species was collected in Costa Rica, and described in 1996 as Cryptothallus hirsutus (now Aneura crumii^[1]).^[11] As of 2008^[update], it had not been observed again.^[5]

Plants have been found in locations across northern Europe, and once in Greenland.^[3] They grow in bogs and are typically found underneath peat moss or other dense moss growth near birch trees.^[6]