The generic name Dermonema was proposed by Greville in an unpublished manuscript on the algae collected in India by Robert Wight (1796--1872), a British surgeon and botanist. It was based on a previously undescribed species, D. dichotomum. Harvey (1857a: no. 93) identified one of his collections from Sri Lanka as this species and published the name, without a description, in his exsiccata, ``Ceylon Algae''. Dickie (1874b: 191) used the name for a record from Mauritius, while G. Murray (1887: 36) applied it to several specimens in the British Museum. The name also appears without description in Schmitz's prospectus of his classification of the Rhodophyceae (Schmitz 1889: 438), where the genus is placed in the tribe Dermonemeae of the family Helminthocladiaceae. A validating description was finally provided by Heydrich (1894: 290--291), who, however, made only one comparative statement, namely, that the spermatangial filaments are produced by subterminal cells of the cortex rather than by terminal cells as in Helminthora. Schmitz, who contributed an account of the nomenclatural history of Dermonema to Heydrich's paper, later provided the definitive character of the genus and of the tribe, namely, a carposporophyte that is diffused through the cortex (published posthumously as Schmitz & Hauptfleisch, 1896: 329).
Meanwhile, Kützing (1867: 1, pl. 1: figs. a--c) published a new species, Gymnophlaea gracilis, for which he gave the provenance as New Caledonia. According to Weber-van Bosse (1921: 204), however, the only specimen of G. gracilis in Kützing's herbarium (in L) is one collected at Galle, Sri Lanka, by Eduard von Martens, the zoologist of the Prussian Expedition to East Asia. The algae resulting from this expedition were published by Eduard's father, Georg von Martens, who initially (1868: 29) identified his son's collection as Gymnophlaea dichotoma (J. Agardh) Kützing (Nemastoma dichotomum J. Agardh), but later in the same publication (1868: 146) decided that it was representative of a new species, G. gracilis. It is clear that Martens had sent Kützing a specimen of his son's collection bearing the manuscript name Gymnophlaea gracilis, and that this specimen, which Kützing annotated ``Tab. Phyc. t. XVII, p.1, tab.1'', is the holotype of G. gracilis Kützing and an isotype of G. gracilis Martens. (The holotype of G. gracilis Martens, at B, was destroyed during World War II.) Whether Kützing's action was an innocent mistake is an unanswered question. The title-page of the account of the algae of the expedition is dated 1866, seemingly rendering G. gracilis Kützing a later homonym of G. gracilis Martens. However, the demonstration by Stafleu & Cowan (1981: 317) that contemporary reviews establish the date of publication of the completed work as January 1868 reverses the relative priority of the two names. The subsequent nomenclatural history of this species, however, makes this relative priority moot.
When Heydrich validated the generic name Dermonema, he realized that Gymnophlaea gracilis Martens was conspecific with the alga distributed by Harvey in his Ceylon exsiccata, but he erroneously assumed that Greville's manuscript name D. dichotomum published by Harvey had priority. He placed the Martens name in synonymy, thereby rendering D. dichotomum Harvey ex Heydrich a superfluous name. Although Heydrich based his description and illustrations on a collection from Taiwan, the name must be typified with the type of G. gracilis Martens in accordance with Art. 7.5.
Schmitz & Hauptfleisch (1896), misled by Kützing, recognized two species in the genus, D. dichotomum from Sri Lanka and D. gracile (Kützing) Schmitz from New Caledonia. Pointing out Kützing's error and realizing that Gymnophlaea gracilis Martens had priority over Dermonema dichotomum, Weber-van Bosse (1921: 204) made the combination Dermonema gracile (Martens) Weber-van Bosse. Because G. gracilis Martens is a later homonym and hence not capable of serving as a basionym, Weber-van Bosse's binomial should be accredited directly to her as a new name. In a detailed study of the structure and reproduction of D. gracile from Sri Lanka, Svedelius (1939: 30) confirmed that the carposporophyte is diffused through the cortex and that spermatangial filaments are borne on subterminal cortical cells.
The conspecificity of D. gracile and Cladosiphon frappieri Montagne & Millardet (1862: 20--21, pl. XXVI: fig. 1; type locality: Réunion) was proposed by Børgesen (1942b: 42), who made the combination Dermonema frappieri (Montagne & Millardet) Børgesen.
Dermonema frappieri was first reported from the Pacific coast of North America by Dawson (1954a: 6--7), who recorded it from three Mexican localities: Mazatlán (Sinaloa), Isla San Benedicto, and Isla Socorro. Dawson (1959a: 8, 9, 19) later found it at Isla Carmen and Isla Ildefonso in the Gulf of California. Subsequent surveys by Mexican phycologists along the tropical Pacific coast of Mexico have shown it to be common on wave-swept rocks in the upper intertidal zone. In the course of a study by Francisco F. Pedroche and Alejandrina vila Ortíz on the structure, reproduction, phenology, and ecology of Dermonema in tropical Pacific Mexico, the question arose as to the identity of Nemalion virens J. Agardh (1847: 8), originally described from a collection made by the Danish botanist Frederik M. Liebmann at San Agustín, between Salina Cruz and Puerto ngel, Oaxaca. The name, without a description, had appeared earlier (Liebmann 1846: 76). Børgesen (1942b: 27) made a ``rather superficial examination'' of an isotype specimen at Copenhagen (C) and found no reproductive structures, but judged the anatomical structure to be as in Nemalion. The only record of N. virens other than the type is a report by Dawson (1953: 36, pl. 1: fig. 4) of a collection from Cabeza Ballena, near Cabo San Lucas, Baja California Sur, Mexico. This collection included male plants, and Dawson described whorled tufts of spermatangia borne on subterminal cells, a feature consistent with Dermonema. Pedroche has confirmed this spermatangial arrangement by examining a specimen from this collection (Dawson 3341) in UC. Through the kindness of Dr. Per Lassen, Curator of the Herbarium at the University of Lund, the type of Nemalion virens was sent to Berkeley for study. The type sheet is annotated ``Nemalion virens J. Ag. Sp. Alg. p. 420.'' in J. Agardh's hand and has mounted on it a card (no. 32094) annotated ``St Augustin Liebmann'' and bearing a complete thallus. Another small card (no. 32095) bearing pieces of branches is housed together with its label in a pocket. (Dawson [l.c.] in error cited the type sheet as 54018.) In habit and anatomy this specimen is unequivocally identical with Mexican Dermonema. Moreover, its morphology is consistent with Dermonema from Sri Lanka as detailed by Svedelius (1939). The earliest epithet-bringing name for this widespread Indo-Pacific species is Nemalion virens J. Agardh.