Rhodoglossum hancockii Dawson

Rhodoglossum hancockii Dawson

Rhodoglossum hancockii Dawson, 1944:304.

The second known collection from the type-locality, Isla San Esteban, was made at a 3–7.6 m depth, 25 Apr 1974, JN-5563 ♀ (US), (leg. JN). This material closely resembles the type collection of Dawson (1944, pl. 71: fig. 1; 1961a). Rhodoglossum is a genus more commonly associated with temperate seas, and, in the Gulf, R. hancockii is apparently restricted to the cooler waters of Las Islas de la Cintura.

Another specimen from Isla San Pedro Nolasco was referred to this species by Dawson (1959). Our examination of this plant (Dawson 18553 (US), 25 Apr 1958) has led us to conclude it is not R. hancockii. It appears to be closely related to the R. affine (Harvey) Kylin (1928) complex of the Pacific coast (see Dawson, 1961a; Smith, 1969). The San Pedro Nolasco specimen differs from R. hancockii by its small size, 4–5 cm tall, and narrow straplike fronds, (1–)2–3(–5) mm wide, which have subacute to blunt tips. New Gulf material is in close agreement with R. hancockii, a species with broadly expanded blades arising from a very short stipe, to 20 cm tall and 5–8(12) cm wide, having dichotomous divisions that narrow in the uppermost portions to acute tips. An additional collection is recorded from the south side of Isla Patos (Dawson, 1949).