Heterocladium flaccidum (Schimp.) A.J.E.Sm.

Hugonnot, Vincent, Osman, Imen Ben, Daoud-Bouattour, Amina, Muller, Serge D., Fedorova, Alina V., Ignatova, Elena A. & Ignatov, Michael S., 2020, A range extension of Heterocladium flaccidum (Schimp.) A. J. E. Sm. to Africa and Asia and confirmation of its specific status, Cryptogamie, Bryologie 20 (21), pp. 265-272 : 267-268

Heterocladium flaccidum (Schimp.) A.J.E.Sm.

(Fig. 3B, G-H, M-N)

SPECIMENS EXAMINED. — North AFrica. Tunisia, Kroumiria, Jendouba Governorate, delegation of Aïn Draham, Oued Zen National Park, Oued Zen, 36°48.43’.08”N, 08°50’.41.34’E, 368 m alt., in deep valley along the watercourse, leg. Vincent Hugonnot and Imen Ben Osman, 4.IV.2019, T2019-150.

Caucasus. Georgia, Adjaria, Mtirala National Park, upper course of Chakvistavi River, c. 4 km upstream of Chakvistavi Village, the buffer zone of the park, 41°40’30.1”N, 41°52’58.1”E, 400 m alt., Broadleaf Colchis forest in the stream valley (right tributary of Chakvistavi River), stones and cliffs along stream, leg. Vadim Bakalin, 12.V.2013, coll. # G-12-23-13. MHA ex VBGI.

DESCRIPTION

Plants

Very slender, forming dull green wiry wefts.

Stems

Irregularly and repeatedly branched (often as a result of apical damage), with fasciculate secondary branching, with weak differentiation of branches and stems; foliage terete to indistinctly complanate.

Branches

Fragile, rupturing at base, at junction with the stem.

Rhizoids

Clustered below leaf insertion, brown, smooth, simple or with a few ramifications, in small fascicles at base of old stems.

Stolons

With distant leaves occasionally present, strongly rhizoidous at apex.

Stem leaves

Erecto-patent, ovate- to lanceolate-triangular, acute, feebly decurrent, 225-290 × 65-110 µm; margins serrate throughout, sometimes more strongly in distal half, or on one side; costa 20-25 µm wide, double or very short and forked distally, reaching 0.2-0.3 the leaf length; alar cells quadrate to oblate in small rectangular ascendant group, 2-3 cells wide; median cells quadrate-hexagonal to ovate, 1-2 times as long as wide, 8-11(-15) × 6-7(-8) µm, with groups of feebly prorate cells dispersed on dorsal side; apical cell triangular, 17-19 × 8-10 µm.

Branch leaves

Similar to stem leaves, but smaller, narrower, and erect to somewhat appressed.

Gametangia or sporophytes

Not observed.

REMARKS

Plants from the Caucasus (Fig. 3A, C-F, I-L) are similar to the Tunisian plants in the narrowly triangular shape of leaves, which are truncate at base and not decurrent, and in sharply serrate leaf margins. However, Caucasian plants are smaller, more irregularly branched; leaves are slightly smaller, 225-260 × 65-100 µm; and laminal cells are more strongly prorate at upper angles on dorsal surface of the leaves. They are very similar in these characters to plants from France and United Kingdom.

HABITAT

In Tunisia, Heterocladium flaccidum was discovered on the banks of a permanent wadi, Oued Zen, in Kroumiria (N.W. Tunisia). Kroumiria is a mountainous massif with alternating sandstone and clay from the Numidian flysch. It is located in the humid Meso-Mediterranean belt but reaches the SupraMediterranean belt at its highest elevations ( INRF 1975). It is the wettest region of Tunisia: rainfall ranges between 1000 and 1500 mm /year, and it regularly snows in the mountains from December to February.Annual average temperatures range from 16 to 20°C, with minimum values between 2-7°C (January), and relatively strong daily, seasonal fluctuations. The regional vegetation is dominated by Quercus suber L. woodlands at low altitudes, and by Q. canariensis Willd. forests at higher elevations. Understoreys are constituted of numerous shrubs, including Arbutus unedo L., Calicotome villosa (Poir.) Link , Erica arborea L., Myrtus communis L., Phillyrea media L. and Pistacia lentiscus L. Despite the summer drought in Kroumiria, the high annual rainfall permits the existence of some permanent watercourses in the central part of the region. In Oued Zen region, the bottom of the valleys and small flat areas are occupied by riparian forests of Alnus glutinosa (L.) Gaertn. Individual Alders extend narrowly and discontinuously along the main axis of wadi beds and do not occur beyond their confines. These riparian forests represent the North-African Campanulo alatae-Alnenion glutinosae classified within the Osmundo-Alnion and the Populetalia albae ( Géhu et al. 1994). The most abundant populations of Heterocladium flaccidum were found at the interface between Alnus glutinosa and Quercus canariensis woodlands, on the higher banks that are characterized by a certain instability and the occurrence of small rock outcrops. These are entangled with aerial roots and trunks. There H. flaccidum grows on soil between rocks and roots. Accompanying bryophyte species are: Calypogeia fissa (L.) Raddi, Dicranella heteromalla (Hedw.) Schimp. , Fissidens serrulatus Brid. , F. taxifolius Hedw. , Homalia lusitanica Schimp. , Isothecium algarvicum W.E.Nicholson & Dixon , Lejeunea cavifolia (Ehrh.) Lindb. , Lophocolea fragrans (Moris & De Not.) Gottsche, Lindenb. & Nees , Lunularia cruciata (L.) Dumort. ex Lindb., Microeurhynchium pumilum (Wilson) Ignatov & Vanderp. , Plagiomnium undulatum (Hedw.) T.J.Kop. , Plagiothecium nemorale (Mitt.) A.Jaeger , Ptychostomum donianum (Grev.) Holyoak & N.Pedersen , Rhynchostegium confertum (Dicks.) Schimp. , Saccogyna viticulosa (L.) Dumort., and Thamnobryum alopecurum (Hedw.) Gangulee.