The Status of the Name Alysium Holtingii C. Agardh, a Red Alga Described from Brazil, and a Depiction of the Type Specimen

The type specimen of the red alga Alysium holtingii C. Agardh, described from Brazil, is located in the Lund Herbarium, and it is depicted for the first time in a publication. It is taxonomically identical to Dichotomaria obtusata (J. Ellis and Solander) Lamarck and thus can be treated as a later taxonomic synonym. Alysium is regarded as congeneric with Dichotomaria.

In recent years the red algal genus Galaxaura Lamouroux (1812) has been shown to be heterogeneous.Tricleocarpa was proposed by Huisman and Borowitzka (1990) as a segregate genus from Galaxaura, and Dichotomaria Lamarck (1816), long regarded as congeneric with Galaxaura, has been reinstated (Huisman et al. 2004).In the ongoing revision of the family Galaxauraceae (Wang et al. 2005), the status of the ill-known genus Alysium deserves attention.Alysium was established by C. Agardh (1823), with the single species A. holtingii C. Agardh ("Ulva holtingii Mert.msc.") from the coast of Brazil, the specimen having been sent by Mertens to Agardh.Although the genus had only a brief description, the single species was provided with a more detailed account.C. Agardh (1824) repeated the name in his 'Systema algarum '. Sprengel (1827) recognized the genus, referring to two species, the original species A. holtingii and a new species, A. perrini Sprengel from the West Indies.But because the legitimate and available name Galaxaura oblongata (J.Ellis and Solander) J.V. Lamouroux was cited after A. perrini, it is an illegitimate name.Léman (1828) referred to Alysium holtingii as a plant from Brazil distinguished by its membranous, hollow, inflated frond, provided with constrictions, giving it an articulated aspect as well as by its reticulate, pentagonal covering.
In their account of Alysium holtingii (as "Hoeltingii"), Martius et al. (1833) said it was discovered by "Hoelting" on the ocean shore near Sebastianópolis.It is not clear how they were able to provide this more precise information about the type locality.
The detailed floristic accounts by Taylor (1960) and Oliveira (1977) made no specific mention of Alysium holtingii C. Agardh, nor did the historical accounts by Taylor (1931) and Joly (1952) refer to C. Agardh's Alysium holtingii.The fact that the type specimen of A. holtingii has never been depicted in the literature motivated me to locate it and also to determine whether its taxonomic assignment lies with Tricleocarpa fragilis or Dichotomaria obtusata.

OBSERVATIONS
The type specimen of Alysium holtingii (Fig. 1) was located in the Agardh Herbarium (as No. 32432) in Lund, Sweden, and received on loan.Label information (Fig. 2a) includes the following words near the specimen: "Ulva holtingii M. ab oris Brasil.Holting 1819" and "Cm.1821" [meaning that it was communicated/sent from Mertens to Agardh in 1821].Also near the species name is "n.p.", which is interpreted as "n.sp.".In the bottom left corner of the sheet (Fig. 2b) are the words: "Alysium holtingii Ag." and "Ulva holtingii Mert."The specimen has a bushy, spreading aspect with an overall height of 5 cm.It is made up of distinctly segmented axes (Fig. 3), with branching from 5 to 8 orders.The branching pattern is dichotomous or sub-dichotomous.The axes appear to be cylindrical rather than flattened but have collapsed due to their hollow nature.Individual segments are 1-2.5 mm in width and 3-5 (-6) mm in length.The specimen appears chalky and bleached, but the distal tips are relatively dark, reflecting the noncalcified condition of these growing regions.The surface of the segments is glabrous.The joints appear to be uncalcified.
A small fragment was excised and treated with dilute HCl to decalcify.Then sections were gently made with a single-edged razor blade.The outer layer of cortical cells were mostly adherent upon decalcification and presented a continuous aspect of polygonal cells (5-, 6-, and 7-sided) in surface view, the cells measuring 20-  28 µm across.Older surface cells were more rounded in outline and ranged from 30-50 µm.There were 2 or 3 layers of cortical cells.In the interior of the thallus were very loosely-organized branching medullary filaments, 10-22 µm in width and of indeterminate length.
The moniliform habit and the collapsed nature of the thallus upon drying conform to the accounts given for Dichotomaria obtusata by various workers, such as Papenfuss et al. (1982), Huisman and Borowitzka (1990), Littler and Littler (2000) (all as Galaxaura obtusata) and Chou (1945, as the taxonomic synonym G. robusta).Huisman and Kurihara (2006) characterized Dichotomaria obtusata as having thalli that are terete throughout and segmented.According to Abbott (1999), the terete axes in this species are "often collapsed", in agreement with the condition in the specimen of Alysium holtingii.In Tricleocarpa, the outer cortical cells become disengaged upon decalcification (Huisman andBorowitzka 1990, Abbott 1999), and the cortical cells become smaller toward the surface (Huisman and Kurihara 2006).These observations allow us to conclude that Alysium holtingii is taxonomically identical to Dichotomaria obtusata and thus can be placed in its synonymy.This confirms the ideas of Decaisne (1842), Kützing (1843), Martens (1870), De Toni (1897), and Kjellman (1900) but not of J. Agardh (1976), who treated the species as identical with Galaxaura oblongata (now Tricleocarpa fragilis).Similarly, Alysium C. Agardh is to be listed as a heterotypic synonym of Dichotomaria.
The illegitimate name Alysium perrini Sprengel (1827), for which the available name Galaxaura oblongata was cited, can be listed in the synonymy of Tricleocarpa fragilis (Linnaeus) Huisman and R.A. Townsend.Huisman and Townsend (1993) demonstrated that Eschara fragilis Linnaeus ( 1758) is an older taxonomic synonym for Corallina oblongata J. Ellis and Solander (1786).

Fig. 2 -
Fig. 2 -Label data: a, words near specimen; b, words at bottom corner of sheet.