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COSEWIC assessment and status report on the Flooded Jellyskin (Leptogium rivulare) in Canada

Species Information

Name and classification

Leptogium rivulare (Ach.) Mont. in Gaudichaud, Bot. Voy. Monde La Bonite: 117 (1846). [nomen sed non planta]. Lichen rivulare Ach., Lich. Suec. Prodr. 131 (1798); type: Sweden (H-Ach 1915B, lectotype designated by Jørgensen & James [1983])

Leptogium crenatellum Tuck. Amer. J. Arts Sci., ser. 2, 28: 200 (1859); type: USA, Vermont, Brattleboro, Frost (FH, holotype; US, isotype).

Leptogium sernanderi Du Rietz, Bot.Notiser 1922: 318 (1922); type: Sweden, Uppland, Knivsta, Noorsån, 27 July 1917, G. Sernander (UPS, lectotype designated by Jørgensen & James [1983]; isolectotypes distributed in Malme, Lich. Suec., no. 851).

English name: Flooded jellyskin lichen (which refers to both the habitat, and the fact that Leptogium, along with the genusCollema, form a group known as the "jelly lichens").

French name: (le) leptoge des terrains inondés.

Classification: Fungi, Ascomycota, Lecanorales (order), Peltigerinae (suborder), Collemataceae (family).

This species, which is in the Leptogium azureumcomplex, is distinctive because of its 4-spored asci and unique habitat. In North America, it was long known as L. crenatellum Tuck. (e.g., Fink 1935, Sierk 1964), but that species was found to be a synonym of L. rivulare by Jørgensen & James (1983), who discussed the nomenclature of the species in some detail. The relevant types have been studied by both the monographer (H.A. Sierk) and by the Norwegian lichenologist Per Magnus Jørgensen.

Description

When dry, Leptogium rivulare is a small grey or bluish-grey foliose lichen that is dotted or speckled with rather minute, light reddish-brown apothecia (Figure 1). The lobes are smooth (without the wrinkles, soredia, or isidia that characterize similar species) and are rounded to somewhat elongate, 0.7 to 3.5 mm wide. The cortex of the upper and lower surfaces consists of a single layer of roundish cells; the medulla is extremely thin. The photobiont is a cyanobacterium (Nostoc).

When wet, the lobes swell with water and become gelatinous and translucent, hence the name “jellyskin” lichen.

Apothecia are commonly produced, sometimes so thickly as to give the lichen a brownish cast. This abundance of apothecia readily distinguishes Leptogium rivulare from the very common, and much larger L. cyanescens (Rabenh.) Korber. The apothecia may be superficial or constricted at the base, 0.4 to 0.6 (but up to 1.2) mm in diameter. The disk is light brown to reddish brown, flat to slightly concave, with margins that are smooth and even, relatively thin, and partly disk-colored, but with an outer layer of grey thalloid tissue. The spores are colourless and multicellular (submuriform, with 3 [or 4] transverse septa and one longitudinal septum [or none at all]). The spores are elliptical, but rather pointed at the tips, and measure 15-21 x 7.5-10 µm. There are consistently 4 spores per ascus.

Figure 1. Individual Leptogium rivulare thallus

Figure 1. IndividualLeptogium rivulare thallus.

Chemistry: No lichen substances are known (Brodo et al. 2001). (A more detailed description is found in Sierk [1964].)