A study (Zander and Hedderson 2016) of Hymenostylium xanthocarpum (Hook.) Brid., an uncommon species now known from Republic of Cameroon, La Reunion, India and Nepal, revealed that this species was quite distinct from the widespread H. recurvirostrum (Hedw.) Dixon and its several related species. A new genus was proposed for the latter, Ardeuma R.H. Zander & Hedd. The distinguishing traits are tabulated here (Table 1).

The second author noticed that the combination in Ardeuma in that paper for Hymenostylium recurvirostrum var. insigne (Dixon) E.B. Bartram was not the earliest available at the species level, and this is here corrected.

Table 1.

Comparison of salient differential features of Ardeuma and Hymenostylium.

Ardeuma annotinum (Mitt, ex Dixon) R.H. Zander & Brinda, comb. nov.

Basionym: Hymenostylium annotinum Mitt, ex Dixon, J. Bot. 48: 308. 1910. Type: Bhutan, India, Griffith 17 (BM! isotype).

Weissia recurvirostra var. insignis Dixon, J. Bot. 40: 377. 1902. Hymenostylium recurvirostrum var. insigne (Dixon) E. B. Bartram, Philipp. J. Sci. 68: 106. 1939. Hymenostylium insigne (Dixon) Podp., Consp. Musc. Eur. 173. 1954. Gymnostomum insigne (Dixon) A.J.E. Sm., J. Bryol. 9: 279. 1976. Ardeuma insigne (Dixon) R.H.Zander & Hedd., J. Bryol. Published online 12 July 2016. Page 5. DOI 10.1080/03736687.2016.1184405.

Ardeuma annotinum differs from its most common congeners by the combination of leaves 2–2.5 mm in length, sharply reflexed above a broad base; distal marginal cells bistratose in patches, laminal papillae mostly bifid, often crowded; costa excurrent, guide cells 4–7, and adaxial epidermal costal cells differentiated, This species, discussed as Hymenostylium annotinum, was treated at length by Zander and Eckel (1982). Several other synonyms are provided by Eckel (2009). Additional discussion and keys to the species in the New World are given by Cano and Jiménez (2013).