ECOLOGY AND TAXONOMY OF Holimeda 147 



produce the illusion of roundness. These edges, in addition, may 

 sometimes create the impression of a matrix, perhaps formed of the 

 covering lamella, surrounding the utricles. This may represent the 

 condition described by Barton for some of these plants. 



Four infraspecific categories have been designated for this species : 

 V. opuntioides (Borgesen, 1911), f. laxa (Barton, 1901), f. elegans 

 (Yamada, 1941), and f. lata (Taylor, 1950). The latter has been trans- 

 ferred to lacunalis (Hillis, 1959). Since the variations in appearance on 

 which the other three forms are based also occur in typical plants, these 

 three forms were placed in synonymy under gracilis (Hillis, 1959). 



Halimeda lacrimosa Howe 



Figure 45. 



Halimeda lacrimosa Howe (1909), p. 93, Plate 4, Fig. 1; Plate 6, Figs 3-11; 

 CoUins (1909-1918), p. 399; Hillis (1959), p. 357, Plates 2, 5-7, 10. 



Plants fragile, straggling and decumbent, to 5 cm long; calcification 

 heavy ; colour on drying white, often becoming bluish-green towards the apex, 

 the surface smooth and usually glossy; branching restricted, generally 

 di- or trichotomous ; segments easily crushed on drying, the basal ones usually 

 cylindrical, often moniloid; others and particularly the more apical ones 

 commonly spherical or tear-shaped, to 5 mm in the three dimensions. 



Cortex of two to three layers of utricles, these often produced by dicho- 

 tomies or tetrachotomies in the lateral branches of the medullary filaments ; 

 outermost utricles usually remaining slightly attached on decalcification, 

 occasionally separating but still appearing hexagonal rather than rounded 

 in surface view, 31-42 [xm in surface diameter, 40-110 [im. long in section, 

 generally 6-18 supported by each secondary utricle; secondary utricles 

 capitate, 66-110 jj.m broad at the apical end, 105-340(-400) [im. long. 



Nodal medullary filaments uniting in twos, threes and fours, incompletely 

 or completely, short and complete fusions often mixed so that fewer filaments 

 may emerge than participate in the fusion ; resultant units not particularly 

 entangled and at most adhering only slightly. 



Type specimen. Bahamas, Mariguana, Howe 5524, 1 1 December, 

 1907 (NY). 



Habitat. Howe (1909) reports this tiny species growing on stones, 

 in sand, and on the stipes of Avrainvillea. It is also associated with 

 Pocockiella (Diaz-Piferrer collection). Its known vertical range is 

 — 1 m to — 20 m. 



Geographic distribution. North-western Atlantic. 



