|Constancea 83, 2002|
University and Jepson Herbaria
P.C. Silva Festschrift
Codium elisabethae O.C. Schmidt, 1929: 103, fig. 8.
O.C. Schmidt, 1931: 21, fig. 24.
Thallus globose or subglobose, hollow, moderately firm, dark green, to 14 cm diam., adherent to substratum by a tuft of rhizoidal attachments. Thallus dissecting out into individual utricles or pairs of utricles, the second utricle being produced directly from the parent utricle; mature utricles of adult thallus subcylindrical to slightly clavate, 265530 µm diam., (2.5) 35.5 (6.7) mm long; apices of utricles broadly rounded but acuminate and slightly asymmetrical; utricular wall 23 µm thick, to 85 µm thick at apex, where it forms a more or less pronounced obtuse mucro; apical wall finely lamellate. Hair scars relatively abundant on certain utricles, forming band 350650 µm below apex. Medullary filaments 60110 (130) µm diam. Gametangia narrowly ellipsoidal to cylindrical, usually tapered anteriorly, 65130 µm diam., 370550 µm long, borne usually one (sometimes two, rarely three) per utricle, on pedicel 1525 µm long, 720840 µm below apex of utricle..
ARQUIPELAGO DA MADEIRA. Ilha do Porto Santo: near Ponta da Calheta, 12 m deep, 16.x.1978, CANCAP Expedition 3, no. 791 (L).
ISLAS CANARIAS. El Veril, Islote de Montaña Clara, north of Isla Lanzarote, 56 m deep, 31.iii.1983, Prud'homme van Reine 8143 (L).
Codium elisabethae is remarkable, not in itself, but in conjunction with C. bursa. The thalli of the two species are indistinguishable externally, the distinction being solely anatomical. Whereas in C. bursa (Fig. 2) occasional utricles may have asymmetrical and somewhat thickened apices, typically the apices are only slightly thickened (625 µm thick), broadly rounded, and not regularly acuminate as in C. elisabethae (Fig. 3).
It might be expected that two such similar species evolved with the help of geographical isolation, and in fact there is almost no overlap in their known ranges. Codium bursa is abundant in the Mediterranean and extends northward in the eastern Atlantic along the coast of France to southern England. It also occurs on Gran Canaria, Lanzarote, and Fuerteventura islands in the Canary Islands. Codium elisabethae, by contrast, has been reported only from the Azores and Madeira and is now recorded from Lanzarote, the most northerly and easterly of the Canary Islands.
Thus, Lanzarote is the only area where the ranges overlap, but it is not known whether there is any site where the two species grow side-by-side. It would be of great interest to know if the two species are reproducing sexually and, if so, whether they are capable of hybridizing. If hybridization is possible and the two species are sympatric, the question arises as to the nature of the ecological barrier that prevents the two species from merging. The high degree of morphological similarity between the two species suggests that correspondingly small molecular differences would be found between the two genomes, but relevant data are not available. Utricles with pointed apices have been shown to occur in several species representing three different sections of the genus (Silva, 1984: 426, fig. 2). One of these is a crustose species, Codium acuminatum O.C. Schmidt, which was originally described from Madagascar and subsequently reported from Mozambique. It differs morphologically from C. arabicum Kützing, a common Indo-Pacific species, only in having pointed utricles. In the latter species the apices of utricles are slightly rounded and often with alveolate or cribrosely pitted walls. As with the C. bursa-C. elisabethae pair of species, it would be interesting to ascertain the molecular distance between C. acuminatum and C. arabicum.
While studying the marine algae of the Azores, Schmidt found only two thalli of C. elisabethae, both from the type locality and both sterile. Recent collections of this species have been made mainly by the CANCAP Expeditions of the Netherlands Council of Sea Research (19781981).
Collecting data on these specimens indicate that C. elisabethae grows subtidally at depths varying from a few centimeters to about 20 m. Gametangia are now described and illustrated for the first time, although Neto (2000: 486) previously reported having found fertile plants in the Azores in October, December, and February.