Usnea subfloridana (images of British lichens)

Fruticose, tufted, much branched, yellow-green to grey-green, black at base of main stem, the main stem just above the base with fine, transverse but not longitudinal cracking, branches not constricted at their bases, terminal branches with rounded to oval soralia and clusters of short, spine-like isidia; apothecia uncommon, variable in size but sometimes large, ringed by untidy, radiating, sorediate branches. Widespread and often very common on tree trunks and more especially on the smaller branches, rare on rocks.

Refs: Nordic Lichen Flora (2011) 4: 125, 170 (photos, printed too dark); James (2003), 29 (line illustrations); Smith et al. (2009), 928; Purvis et al. (1992), 628; Dobson (2005), 447 (photo); Dobson (2011), 453-4 (photo); Whelan (2011), 149 (photo); Tõrra & Randlane (2007), 420 (photo), 430; van Herk & Aptroot (2004, 2013), 374-5 (photo); Valcárcel et al. (2003), 372-3 (photo); Wirth (1995), 2: 943, 952 (photo); Wirth et al. (2004), 36 (photo); Wirth, Hauck & Schulz (2013), 2: 1135, 1139 (photo); Moberg & Holmåson (1984), 109 (photo); Holien & Tønsberg (2008), 68 (photo); Stenroos et al. (2011), 482-3 (photo); Hinds & Hinds (2007), 507 (photo); Walewski (2007), 138 (photo).

Generally the commonest Usnea species with a black base to the stem, but requires care in checking other identification characters. The poorly known but evidently widespread U. wasmuthii looks near identical in the field and may grow intermixed with U. subfloridana, but differs in having very minute longitudinal as well as more obvious transverse cracks in the cortex of the main stem just above the base, and in its chemistry. U. glabrescens is also very similar but lacks isidia (but as do immature thalli of U. subfloridana!). Fertile specimens of U. subfloridana resemble the closely related U. florida, but the latter lacks soredia and isidia in its upper branches and its apothecia have a neater, almost 'flower-like' appearance.

Recent molecular work has suggested that this species is not distinct from U. florida, and, if so, the name becomes a synonym of that species. However, in view of the apparent distinctness of the true "florida morphotype" and the fact that it has been understood to be a rare, ecologically distinct and declining taxon, it could be a major conservation headache if numerous records of U. subfloridana were assigned to U. florida before the correlation of micro-morphology and apparent cladistic position is better understood. I am following the treatments by James, in Smith et al. (2009), and Clerc, in Nordic Lichen Flora 4 (2011) here.

Host to the lichenicolous fungus, Biatoropsis usnearum.

FGBI: http://fungi.myspecies.info/all-fungi/usnea-subfloridana

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Images of British Lichens