Revision of Dawson's collections referred to Lithothamnion lamellatum (Melobesioideae, Corallinales, Rhodophyta)
Fifteen collections from the herbarium Dawson, previously housed at the Natural History Museum of Los Angeles County and now moved to the University Herbarium, University of California, are re-examined. The material represents coralline algae collected between Pescadero Point (Monterey County, California) and Punta Malarrimo (Baja Vizcaino, Pacific Mexico), most of them cited by Dawson (1960) in his account of Lithothamnion lamellatum Setchell et Foslie from Pacific Mexico. No specimens of Mesophyllum (Lithothamnion) lamellatum (Setchell et Foslie) W.H.Adey are identified in these collections that instead include material of at least five new species, herein described as Leptophytum helenae sp. nov., L. hyperandri sp. nov., L. kymatodes sp. nov., Mesophyllum megagastri sp. nov., and M. stenopon sp. nov. The most common species in the collections is Leptophytum julieae Athanasiadis et W.H.Adey (2006), originally described from Vancouver and the Queen Charlotte Islands, and which expands its southern distribution between Punta Malarrimo (Baja Vizcaino) and La Jolla (California). It is also shown that tetrasporangial thalli of Mesophyllum crassiusculum (Foslie) Lebednik from Pacific Mexico (Cortez Bank) possess specialized (thinner-wider) pore cells.