Riccia okahandjana Arnell, 1957

Riccia okahandjana Arnell View in CoL , in Mitteilungen der Botanischen Staatssammlung München 16: 268 (1957).

Type: Namibia: Bez. Otjiwarongo: Okosongomingo , Volk 1944( lecto, designated by Perold, 1993: PRE-CH 4233 !) .

Plants observed in nature.

Plants prostrate, growing crowded in gregarious patches or in rosettes, 10–30 mm in diameter. Thallus when moist glaucous green to bluish green; dark purple scales projecting vertically above margins; when dry, dorsally yellowish green. Whole plants 5–10 mm long. Segments narrowly ovate or linear to ligulate, up to 5.2 mm long, 1.0– 1.5 mm wide; in cross section segments almost twice as broad as high. Ventral flanks steep, covered by scales, margins crenate. Branches simple, once or twice furcate. Dorsal groove present, narrow and deep apically, shallow and wider proximally, disappearing towards base. Scales conspicuous, rounded, imbricate, partially overlapping the next scale, 280–450 x 350–560 µm, projecting above thallus margin, often hyaline toward base, rarely to margin, dark purple colored. Cilia absent. Dorsal epidermal cells bistratose, thin walled up to 38 µm wide and up to 66 µm high. Cells conical or somewhat elongate and sometimes mamillate due to constrictions in the middle. Photosynthetic tissue consisting of vertical columns of 6–8 isodiametric to short rectangular cells enclosing narrow elongate air chambers, storage tissue occupying ventral region with rounded cells, irregularly arranged.

Monoicous. Archegonia are in the dorsal groove with dark purple necks up to 110 µm long. Antheridia not seen. Capsules numerous, bulging from the dorsal surface, dorsal surface eventually disintegrating with maturity leaving sharp-edged open holes in the thallus filled with spores. Spore s 90–93 µm in diameter, globose to triangularglobose in polar view, tetrahedral in equatorial view; light golden when young or straw-colored, golden brown when mature, wingless, perforated at marginal angles, margin crenulate; ornamentation the same on both faces, densely vermiculate and papillate, papillate projections discrete or several joined together to form short vermiculate ridges, smooth, rounded; distal face convex, proximal face with an indistinct triradiate mark, somewhat flattened to shallowly tetrahedral. Figs. 1 View FIGURE 1 , 2 View FIGURE 2 .

Specimens examined

INDIA. TAMIL NADU: Dharmapuri District. Grounds of P.D.R.V. College of Education . 09 January 2020, Suresh N, Abarna 003, Abarna 004. ( MH)

Habitat and phenology

Terrestrial, growing on black and red sandy loam soil crowded in exposed, degraded sites in complete or incomplete rosettes. Plants observed growing during the rainy season months of October to November.

Distribution

In India known only from the grounds of the P.D.R. Vellachiyammal College of Education at Sekkampatti village, Harur, Dharmapuri district, Tamil Nadu, India ( Fig. 3 View FIGURE 3 ). Riccia okahandjana has also been recorded from Africa, occurring in Angola, Botswana, Malawi, Mozambique, Rwanda, South Africa, Tanzania, Uganda, Zaire and Zimbabwe ( Perold, 1999) and has also been reported from the Arabian Peninsula ( Frey & Kurschner, 1988).

(Maps obtained from d-maps website: https://d-maps.com/pays.php?num_pay=84&lang=en accessed on 22 nd Dec 2021).

Affinities

Morphologically, R. okahandjana is similar to the Indian endemic R.coracina Jovet-Ast (2003: 212) and the widespread R. boliviensis Jovet-Ast which was recently discovered in the Eastern Ghats of Andar Pradesh, India ( Asthana & Srivastava, 2020). Jovet-Ast noted the similarity between the two species in her original description of R. coracina ( Jovet-Ast 2003) . However, R. okahandjana differs from R. coracina in several characters, including dorsal epidermal cell layers: bistratose in R. okahandjana ( Fig. 1H View FIGURE 1 ) vs unistratose in R. coracina . They also differ in the colour of the ventral scales, which are purple ( Fig. 1I View FIGURE 1 ) in R. okahandjana vs dark red to black in R. coracina ( Jovet-Ast, 2003) . The spore patterning of the two species is similar; however, they differ in size; with the spores of the Indian population of R. okahandjana only 90–93 µm in diameter vs those of R. coracina which are much larger at 110–130 µm in diameter ( Jovet-Ast, 2003).

While Riccia okahandjana and R. boliviensis both share comparable spore patterns and violet-black scales, R. okahandjana differs from R. boliviensis by the number of dorsal epidermal cell layers: bistratose for R. okahandjana vs unistratose in R. boliviensis is. Spores are also larger in R. boliviensis , 96–120 µm vs 90–93 µm in R. okahandjana . Riccia okahandjana is also distinctive in the disintegration of the dorsal surface of the mature capsule of the fertile gametophyte. In this species, a distinct hole with clearly defined edges ( Fig. 1D & F View FIGURE 1 ) (see also Perold, 1999, Plate 18B) differs markedly from the irregular cavities seen in R. boliviensis and R. coracina ( Perold 1999) .

Notes

The distribution of Riccia okahandjana is also of interest. Several species of bryophytes with disjunct distributions elsewhere in the world have been recorded for India: Notothylas dissecta Stephani (1917: 1020) from Guatemala ( Udar & Singh, 1979), Fissidens neomagofukui Iwatsuki & Suzuki (2002: 165) from Japan ( Daniels et al., 2017), and Trachyphyllum borgenii ( Renauld & Cardot 1897: 226) Brotherus (1909: 890) from Madagascar ( Gupta & Asthana, 2019). This is the second disjunct record of a Riccia species on the Indian subcontinent. Another Indian species with a disjunct distribution includes R. boliviensis ( Asthana & Srivastava, 2020) which is disjunct between South America and India. Whether the disjunct Paleotropical distribution of R. okahandjana between Africa, (and potentially also the Arabian Peninsula) and India is due to vicariance or long distance dispersal is still to be tested. However, the large spores typical of Riccia species are less likely to be wind dispersed, but more likely by water, animal or human dispersal ( Bischler & Jovet-Ast, 1981). It may also be more widespread than currently recorded. Vegetative features are similar to a number of species already discussed, and if collections are sterile, may be misidentified or not identified to species at all.

Perold (1993, 1999) records Riccia okahandjana as having been lectotypified by Perold (1991). However, Perold’s 1991 PhD thesis is not effectively published under ICN Art. 30.9 ( Turland et al., 2018), and the name is not Lectotypified in that work. Lectotypification of Riccia okahandjana is effected by Perold (1993), in accordance with ICN Art. 7.11.