Afroriccardia comosa (Steph.) Reeb & Gradst.

Lucile Rabeau, S. Robbert Gradstein, Jean-Yves Dubuisson, Martin Nebel, Dietmar Quandt & Catherine Reeb, 2017, New insights into the phylogeny and relationships within the worldwide genus Riccardia (Aneuraceae, Marchantiophytina), European Journal of Taxonomy 273, pp. 1-26 : 11-13

Afroriccardia comosa (Steph.) Reeb & Gradst. comb. nov.

Figs 3–4

Aneura comosa Steph. , Botanical Gazette 15 (11): 281. ( Stephani 1890). – Riccardia comosa (Steph.) E.W.Jones, Transactions of the British Bryological Society 3: 74. ( Jones 1956, nom. inval.). – Type: France, La Réunion, 1889, Rodriguez s.n. (holo-: G-00045027!; iso-: PC-0103522!).

Material examined

MADAGASCAR: Angavokely Forest , humid rocks in caves, 18°55′16″ S, 47°44′30″ E, 1600 m, 2 Feb. 2011, Reeb CR 11188 ( PC, TAN) ; Zahamena National Park, river crossing the camp , on rocks, 17°38′19″ S, 48°36′46″ E, 1156 m, 28 Dec. 2013, Reeb & Andriamanantena, CR13Z28 , CR13Z32 ( PC, TAN) ; Zahamena National Park , on seeping rocks, highest part of the river crossing the camp , 17°38′22″ S, 48°38′45.3″ E, 1294 m, 30 Dec. 2013, Reeb & Andriamanantena CR13Z55 ( PC, TAN) .

FRANCE, LA RÉUNION: “ Sur les mousses, source pétrifiante de Hell-Bourge ”, G. de l’Isle 220 ( PC- 0716023 ); “ sous Piton de la Fournaise, le long GR2 , Réserve de Mare Longue ”, 21°20′30″ S, 55°44′30″ E, 175–300 m, Vojko 9435B ( EGR); without details, De Lisle, De Lisle 570bis (PC-0716024 - G 00264057 ); Rodrigues s.d., s.n. ( G-00264058 ); “plaine des palmistes”, s.d., s.col. 56 ( PC-0716026 ).

MAURITIUS: Without details, Rodrigues s.d. s.n. ( PC-0716025 ).

UGANDA: Bwindi National Park, Rukungiri, “ Kitahurira bridge. Damp rock surface by stream, shaded site in forest ”, 1480 m, 30 Jan. 1996, Wigginton U5039A ( E-00430553 ).

Description

Dioicous. Thallus green, to 7 cm long, main axes 2.5–4.0 mm wide, creeping, ± regularly (bi-)pinnate, with 1–2 reiterations, branches alternate to subopposite, stolons not observed. Rhizoids developing over the whole width of the ventral surface of the thallus. Main axes plano-convex to biconvex, 6–8(–10) cells thick, margin entire, acute to rounded, un-winged, epidermal cells in cross section 1.5–2.0 × smaller than medullary cells, all cells thin-walled. Terminal branches to 8 mm long, 0.8–2.0 mm wide, 4–5 cells thick, with a conspicuous, 3–4(–6) cells wide wing, branch margins parallel, crenulate, thallus surface cells becoming smaller towards the margin, not or slightly bulging; branch apex rounded to truncate and usually narrowly incised (to 130 µm deep). Mucilage papillae on branches ca 20, present below the apex and in four rows on the ventral branch surface.

Female branches solitary or grouped on main axes and primary branches, 0.5–1.0 mm long, archegonia (unfertilized ones seen only) in pairs, covered by a dense cluster of rhizoids originating from beneath the apex of the female branches, rhizoids up to 0.7 mm long, with strongly thick-walled tips. Multicellular paraphyses lacking. Male branches, calyptra and sporophyte not seen. Vegetative reproduction not observed.

Distribution

Afroriccardia comosa is a rare species that was known only from a few old, 19th century collections from La Réunion and Mauritius; the species is newly reported here from Madagascar and Uganda. The species occurs in evergreen humid forest at mid-montane elevations in Uganda and Madagascar (1100– 1600 m), and at lower elevations in La Réunion (175–300 m). Where habitat information is available, it was always collected on damp rock surfaces, in shaded places, close to water beds (shaded rivers, entrance of caves with water).

Figures

Fig. 3. Afroriccardia comosa (Steph.) Reeb & Gradst. comb. nov. Population close to sample CR 13 Z 28, Zahamena National Park, Alaotra-Mangoro, Madagascar, 17 ° 37 ′ 19 ″ S, 48 ° 37 ′ 46 ″ E, altitude 1196 m. A. Photographs of the thallus. B. Magnified view of the thallus showing solitary female branches (red arrows). Scale bars = 1 cm.

Fig. 4. Afroriccardia comosa (Steph.) Reeb & Gradst. comb. nov. A. Habit of the thallus, Wigginton U 5039 a, Reeb & Andriamanantena CR 13 Z 28. B. Ventral face showing the wide insertion of rhizoids, DeLisle 220. C. Cross section of main axis showing variability in the thickening of cell walls, Reeb & Andriamanantena CR 13 Z 28, holotype G 0045027. D. Cross section of ultimate branch, holotype G 0045027. E. Detail of female branch with dense cluster of rhizoids, holotype G 0045027. Scale bars: A – B = 1 mm; C = 100 µm.