Collema
{{Short description|Genus of lichens}}
{{Automatic taxobox
| image = Collema flaccidum (Ach.) Ach 316011.jpg
| image_caption = Collema flaccidum
| taxon = Collema
| authority = Weber ex F.H.Wigg. (1780)
| type_species = Collema lactuca
| type_species_authority = (Weber) Weber ex F.H.Wigg. (1780)
| synonyms = {{Collapsible list|bullets=on
|Chiastosporum {{small|Dughi (1956)}}
|Collema {{small|P.Browne (1756)}}
|Collema sect. Collemodiopsis {{small|Vain. (1890)}}
|Collema sect. Eucollema {{small|Tuck. (1872)}}
|Collema subgen. Lathagrium {{small|Ach. (1810)}}
|Collematomyces {{small|E.A.Thomas ex Cif. & Tomas. (1953)}}
|Collemis {{small|Clem. (1931)}}
|Collemodiopsis {{small|(Vain.) B.de Lesd. (1910)}}
|Dicollema {{small|Clem. (1909)}}
|Eucollema {{small|(Tuck.) Horw. (1912)}}
|Kolman {{small|Adans. (1763)}}
|Synechoblastus {{small|Trevis. (1853)}}
|Tichodea {{small|Körb. (1848)}}
}}
| subdivision_ranks = Species
| subdivision =
}}
Collema (jelly lichen) is a genus of lichens in the family Collemataceae. The photobiont is the cyanobacterium genus Nostoc.Dobson, F.S. (2000) Lichens, an illustrated guide to the British and Irish species. 4th edition. Richmond publishing Co., Slough, England. Species in this genus typically grow on nutrient-rich bark or somewhat siliceous or calcareous rocks in humid environments.
Description
Collema lichens are characterized by their medium to large size, with a diameter of {{convert|3|to|20|cm|in|abbr=on|0}}. They have a leaf-like, membranous structure that does not swell noticeably when wet. The upper surface of the thallus is dark olive-green to brown-black and is not hairy. The {{lichengloss|lobes}} are 2 to 15 mm broad, rounded, and usually flat or partially raised, with smooth or {{lichengloss|pustulate}} surfaces adorned with elongated ridges or folds.
Both upper and lower {{lichengloss|cortex}} are absent in Collema, and the photobiont Nostoc forms chains of cells throughout the thallus without creating a separate {{lichengloss|photobiont layer|layer}}. Isidia can be present or absent, while soredia are not found in this genus. The reproductive structures, known as apothecia, have a pale brown to red-brown {{lichengloss|disc}} that can be flat or convex. The {{lichengloss|thalline margin}} is whole and sometimes displays isidia.
The {{lichengloss|true exciple}} consists of cells that can be either uniformly sized or elongated. The {{lichengloss|epithecium}} is indistinct and can be colourless or pigmented, while the hymenium is colorless and turns blue when treated with iodine. A more or less colourless {{lichengloss|hypothecium}} is also present. The {{lichengloss|hamathecium}} comprises paraphyses that separate in a solution of potassium hydroxide and may be unbranched or branched, often connecting near their tips, which can be club-shaped or round and exhibit a yellowish to reddish-brown hue.
The asci are club-shaped (clavate) with a strongly thickened apex, and both the {{lichengloss|apical dome}} and the downwardly projecting annulus and apical cap react blue to iodine. Each ascus produces eight spores that are narrowly ellipsoidal to spindle-shaped or nearly cylindrical with transverse septa. {{lichengloss|Conidiomata}}, or {{lichengloss|pycnidia}}, are immersed within the thallus and can be located on the margins or lamina with a pale ostiole. The {{lichengloss|conidia}} are rod-shaped with a slightly enlarged apex. No lichen products have been detected in Collema using thin-layer chromatography.
Species
{{As of|2023|April}}, Species Fungorum (in the Catalogue of Life) accepts 24 species of Collema.
File:Collema subconveniens 1272916.jpg
File:Collema subflaccidum Degel 408008.jpg
- Collema actinoptychum {{small|Nyl. (1868)}}
- Collema coniophilum {{small|Goward (2009)}} – Canada
- Collema flaccidum {{small|(Ach.) Ach. (1810)}}
- Collema furfuraceum {{small|(Schaer.) Du Rietz (1929)}}
- Collema glaucophthalmum {{small|Nyl. (1858)}}
- Collema glebulentum {{small|(Nyl. ex Cromb.) Degel. (1952)}}
- Collema implicatum {{small|Nyl. (1863)}}
- Collema insulare {{small|Degel. (1974)}}
- Collema japonicum {{small|(Müll.Arg.) Hue (1898)}}
- Collema laeve {{small|Hook.f. & Taylor (1844)}}
- Collema leptaleum {{small|Tuck. (1866)}}
- Collema leucocarpum {{small|Hook.f. & Taylor (1844)}}
- Collema marginale {{small|(Huds.) Hoffm. (1794)}}
- Collema nigrescens {{small|(Huds.) DC. (1805)}}
- Collema pulcellum {{small|Ach. (1814)}}
- Collema pustulatum {{small|Ach. (1814)}}
- Collema rugosum {{small|Kremp. (1870)}}
- Collema ryssoleum {{small|(Tuck.) A.Schneid. (1872)}}
- Collema sichuanense {{small|H.J.Liu & J.C.Wei (2003))}} – China
- Collema subconveniens {{small|Nyl. (1888)}}
- Collema subflaccidum {{small|Degel. (1974)}}
- Collema subnigrescens {{small|Degel. (1954)}}
- Collema substipitatum {{small|Zahlbr. (1930)}}
References
{{Reflist|colwidth=30em|refs=
{{Catalogue of Life |id=3SBC |title=Collema |access-date=19 April 2023}}
{{cite web |title=Synonymy: Collema Weber ex F.H. Wigg., Prim. fl. holsat. (Kiliae): 89 (1780) |url=http://www.speciesfungorum.org/Names/SynSpecies.asp?RecordID=1175 |publisher=Species Fungorum |access-date=2 April 2021}}
}}
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