Dendrocollybia Racemosa

''Dendrocollybia'' is a fungal genus in the family Tricholomataceae of the order Agaricales. It is a monotypic genus, containing the single species ''Dendrocollybia racemosa'', commonly known as the branched Collybia or the branched shanklet. The somewhat rare species is found in the Northern Hemisphere, including the Pacific Northwest region of western North America, and Europe, where it is included in several Regional Red Lists. It usually grows on the decaying fruit bodies of other agarics—such as ''Lactarius'' and ''Russula''—although the host mushrooms may be decayed to the point of being difficult to recognize.

''Dendrocollybia racemosa'' fruit bodies have small pale grayish-white or grayish-brown caps up to wide, and thin stems up to long. The species is characterized by its unusual stem, which is covered with short lateral branches. The branches often produce spherical slimeheads of translucent conidiophores on their swollen tips. The conidiophores produce conidia (asexual spores) by mitosis. Because the fungus can rely on either sexual or asexual modes of reproduction, fruit bodies sometimes have reduced or even missing caps. The unusual stems originate from black pea-sized structures called sclerotia. The anamorphic form of the fungus, known as '' Tilachlidiopsis racemosa'', is missing the sexual stage of its life cycle. It can reproduce at relatively low temperatures, an adaptation believed to improve its ability to grow quickly and fruit on decomposing mushrooms.

Taxonomy and phylogeny

The genus ''Dendrocollybia'' was first described in 2001, to accommodate the species previously known as ''Collybia racemosa''. Before then, the so-named taxon was considered to be one of four species of '' Collybia'', a genus which had itself been redefined and reduced in 1997, when most of its species were transferred to ''Gymnopus'' and '' Rhodocollybia''. ''C. racemosa'' was originally described and named ''Agaricus racemosus'' by Christian Hendrik Persoon in 1797, and sanctioned under that name by Elias Magnus Fries in 1821. In his ''Systema Mycologicum'', Fries classified it in his "tribe" ''Collybia'' along with all other similar small, white-spored species with a convex cap and a fragile stem. In 1873 Lucien Quélet raised Fries' tribe ''Collybia'' to generic rank. Samuel Frederick Gray called the species ''Mycena racemosa'' in his 1821 ''Natural Arrangement of British Plants''; both this name and Joanne Lennox's 1979 ''Microcollybia racemosa'' are considered synonyms.

Rolf Singer's fourth edition (1986) of his comprehensive ''Agaricales in Modern Taxonomy'' included ''Collybia racemosa'' in section ''Collybia'', in addition to the three species that currently comprise the genus ''Collybia'': '' C. tuberosa'', '' C. cirrhata'' and '' C. cookei''. A phylogenetic analysis of the internal transcribed spacer sequences of ribosomal DNA by Karen Hughes and colleagues showed that ''C. tuberosa'', ''C. cirrhata'' and ''C. cookei'' form a monophyletic group within a larger ''Lyophyllum''–''Tricholoma''–''Collybia'' clade that includes several species of ''Lyophyllum'', ''Tricholoma'', ''Lepista'', '' Hypsizygus'' and the species ''C. racemosa''. Hughes and colleagues could not identify a clade that included all four species of ''Collybia''. Restriction fragment length polymorphism analysis of the ribosomal DNA from the four species corroborated the results obtained from phylogenetic analysis. Based on these results, as well as differences in characteristics such as the presence of unique stem projections, fruit body pigmentation, and macrochemical reactions, they circumscribed the new genus ''Dendrocollybia'' to contain ''C. racemosa''.

The fungus is commonly known as the branched Collybia, or the branched shanklet; Samuel Gray referred to it as the "racemelike high-stool". The specific epithet ''racemosa'' is from the Latin word ''racemus''—"a cluster of grapes".

Description

From Esenbeck's ''Das System der Pilze und Schwämme'' (1816)
The cap of ''Dendrocollybia racemosa'' is typically between in diameter, and depending on its stage of development, may be conic to convex, or in maturity, somewhat flattened with a slight rounded central elevation (an umbo). The cap surface is dry and opaque, with a silky texture; its color in the center is fuscous