The order Sphærococcoideæ contains red or purple sea weeds with unjointed cartilaginous or membranaceous fronds, composed of many-sided, elongated cells, with spores in necklace-like strings, lodged in external conceptacles. The typical genus (Sphærococcus) contains the Buck’s-horn sea weed which grows at and beyond low-water mark on the south and west coasts, where it is sometimes washed up on the beach during storms. Its fronds are flattened and two-edged, freely branched, and the upper branches are repeatedly forked, and terminate in fan-shaped, cleft branchlets. Both branches and branchlets are fringed with slender cilia, in which the spores are embedded. It is a handsome weed, of a bright-red colour and a somewhat coral-like form.
Allied to this is Gelidium corneum, with flattened, horny fronds, repeatedly pinnate, with the smallest branchlets obtuse and narrower at the base. The spores are contained in conceptacles near the extremities of the branchlets, and the tetraspores are imbedded in club-shaped branchlets. There are a large number of varieties of this species, differing in form, size, and the mode of branching of the fronds. The size varies from one to five or six inches, and the colour is red or reddish green.
In the genus Gracilaria the frond is thick and horny, and the surface cells are very small, while the central ones are large. The spores, formed on necklace-like threads, are enclosed in sessile conceptacles along the branches, and the tetraspores are imbedded among the surface cells of the fronds. The only common species is G. confervoides, with cylindrical cartilaginous fronds bearing long thread-like branches, sometimes reaching a length of two feet. The spore conceptacles are situated on the slender branches, giving them a knotted or beaded appearance. The colour is a dark purple, which rapidly fades when the weed is placed in fresh water or left exposed to the air. Two other species—G. multipartita and G. compressa—are rare.
Calliblepharis ciliata, perhaps more commonly known as Rhodymenia ciliata, has a branching root, short round stem, and a broad, crisp frond that is generally ciliated. Sometimes the frond is simple and lanceolate, with small leaf-like appendages on its edge; and sometimes it is deeply cleft. The spores are arranged in beaded threads in sessile conceptacles on the marginal leaflets. Another species of the same genus (C. jubata) is very similar in structure, but is of a duller-red colour, gradually changing to olive green at the tips; and it has its tetraspores in the cilia only, while in C. ciliata they are collected in patches in all parts of the frond. Both species grow in deep water, and are frequently washed up during storms.
The large genus Nitophyllum contains some beautiful rose-red sea weeds, with irregularly cleft membranaceous fronds, either veinless, or with a few indistinctly visible veins only at the base. The spores are in rounded sessile conceptacles scattered on the surface of the frond; and the tetraspores occur in clusters similarly scattered.
One of the species—N. laceratum—so called from the torn and jagged appearance of the frond, is represented on [Plate VII]. The fronds are attached to a disc-like root, and are very variable in form, being sometimes so narrow as to appear almost threadlike. The plant grows on rocks and large weeds in the lower rock pools and in deep water. In the same genus we have N. punctatum, with broad pink fronds, dotted all over with spore-conceptacles and dark-red clusters of tetraspores; also a few other less common species that are seldom seen except after storms, as they grow almost exclusively in deep water.
The genus Delesseria contains some beautiful rose-coloured and reddish-brown weeds with delicate, leaf-like, symmetrical fronds, each of which has a darker midrib from which issue transverse veins. The spores are arranged like minute necklaces, and are contained in sessile conceptacles either on the midrib of the frond or on leaflets that grow from the midrib. The tetraspores are in clusters which are scattered over the frond or on its leaflets. The algæ of this genus are seldom found growing between the tide-marks, as they generally thrive in deep water, but splendid specimens are often washed up on the beach during storms, especially on the south and south-west coasts.
Fig. 252.—Delesseria alata