Parmotrema thomsonii (Stirt.) A. Crespo, Divakar & Elix (2010a: 1746) MycoBank

Masson, Didier, Magain, Nicolas & Sérusiaux, Emmanuël, 2024, Small island but great diversity: thirty six species of Parmotrema (Parmeliaceae, lichenized Ascomycota), including sixteen new species, on Réunion (Mascarenes), with additional data from the Western Indian Ocean, Phytotaxa 657 (1), pp. 1-138 : 117

Parmotrema thomsonii (Stirt.) A. Crespo, Divakar & Elix (2010a: 1746) MycoBank no. 516755

Platysma thomsonii Stirt. (1879: 321) MycoBank no. 401623

Type:— INDIA. West Bengal: near Darjeeling, s.d., J.A. Thomson 36 ( GLAM, n.v., holotype; fide Awasthi 1987) .

= Parmelia pachysperma Hue (1899: 178) MycoBank no. 398000

Type:— FRANCE. La Réunion: Mafate, 1889, frère Rodriguez s.n. (MNHN-PC-PC0728354!, holotype; fide Culberson 1962) .

Hue (1899) described Parmelia pachysperma from a single specimen sent by frère Rodriguez (= E.A. Marquet) from Réunion. Examination of the type specimen by Culberson (1962) revealed that P. pachysperma was a junior synonym of Platysma thomsonii described twenty years earlier ( Stirton 1879). Later on, Awasthi (1987) showed that this species was not homogeneous but comprised two distinct taxa, Parmelaria thomsonii (Stirt.) D.D. Awasthi and P. subthomsonii D.D. Awasthi , differing, in particular, in ascospore size, epispore thickness, and the apothecial disc, perforate or not ( Awasthi 1987, 2007). Both species are unusual as they combine a general parmelioid habit with a cetrarioid feature, namely the presence of conspicuous verruciform marginal pycnidia with gaping ostiole ( Fig. 43B ) ( Culberson 1962, Awasthi 1987). Molecular data further showed that both species belong to the genus Parmotrema ( Crespo et al. 2010a) , as suspected by Culberson (1962).

Examination of the holotype of Parmelia pachysperma ( Fig. 43A & 43B ) confirms Hue’s description and that it belongs to Parmotrema thomsonii , not to P. subthomsonii (D.D. Awasthi) A. Crespo, Divakar & Elix. The disc of the apothecia is perforate, the ascospores are large [(24.5)25– 29.2 –33 × 14.5– 16.6 –19 µm, Q = (1.42)1.52– 1.77 – 2.02(2.06), n = 30], and the epispore wide [(3.5)– 4.2 –(5) µm thick]. The label on the holotype, written in Hue’s hand, reads ‘Legit fr. Rodriguez à Mafate, Bourbon, 1889’. The name of the locality (Mafate or Mafatte) refers either to a small spa village established in the second half of the 19 th century and abandoned since 1913 ( Vidal 2020), or to the whole of the cirque surrounding it and which bears its name. The Cirque de Mafate has been very little studied by lichenologists ( Fig. 1B ), and this may be the reason why P. thomsonii has not been refound on Réunion since 1889. Elsewhere, the species has mainly been reported from the Himalayas (1400–3900 m elevation) in India and Nepal ( Awasthi 1987, Sinha & Singh 2005), and also occurs in the mountains of northern Thailand ( Wolseley et al. 2002). Therefore, the single report from Réunion Island is puzzling. However, among the lichens collected by frère Rodriguez in Mafate in 1889 and studied by Hue (1899) is a unique collection of Hypotrachyna cf. cirrhata (Fr.) Divakar, A. Crespo, Sipman, Elix & Lumbsch (Culberson & Culberson 1981) , a parmelioid taxon with an ecology quite similar to that of P. thomsonii , and probably also with Asian affinities ( Wang et al. 2020). Like P. thomsonii , it has never been found again from the island after 1889.

Figures

FIGURE 1. A: Shade relief map of Réunion Island showing the location of the two volcanic massifs as well as the delimitation of the windward and leeward zones (adapted from Strasberg et al. 2005); B: Distribution of collection sites for the Parmotrema species studied (UTM 2×2 km grid system). Scale bar: 10 km.

FIGURE 43. Parmotrema thomsonii (holotype of Parmelia pachysperma). A: Part of thallus with a mature apothecium; B: Lobes with white-maculate upper surface, and conspicuous verruciform marginal pycnidia with whitish ostiolar region. Scale bars: A = 5 mm; B = 2 mm.