ECOLOGY AND TAXONOMY OF HaUmeda 103 



cylindrical ones, the lengths of which rarely exceed twice the diameter, 

 unlike similar segments in monile and cylindracea which, in general, are 

 at least four times as long as broad. 



Histologically, the thickened walls of the peripheral utricles of 

 stuposa are generally fairly conspicuous in mature segments, particu- 

 larly as viewed from the surface. This thickening is extremely well 

 developed in basal segments where the utricles usually separate on 

 decalcification. Towards the plant apex the induration is less pronounced 

 and the utricles remain more firmly attached after decalcification. 

 Although such thickening may occur in other species, particularly in 

 basal segments, it is generally not as constant a feature as in stuposa. 



HaUmeda simulans Howe 



Figure 26. 



HaUmeda simulans Howe (1907), p. 503, Plate 29; Collins (1909-1918), 

 p. 401; Taylor (1928), p. 84, Plate 10, Pig. 12; Plate 11, Figs 18-19; 

 HilHs (1959), p. 368, Plates 3, 5, 6, 11. 



HaUmeda incrassata v. simulans Borgesen (1911), p. 144, Fig. 11; Borgesen 

 (1913), p. 114, Fig. 92. 



Plants erect, compact, forming cushion-like clumps, to 12 cm tall exclud- 

 ing the holdfast region which may extend to 4 cm ; calcification moderately 

 heavy; branching complanate, frequent, mainly di- to tetrachotomous ; 

 stalk region sometimes moderately well developed, resulting from the fusion 

 of small adjacent segments, more commonly short and rather inconspicuous, 

 of two to three cylindrical to subcuneate or at times reniform segments, the 

 upper one supporting several subcuneate segments which often have an 

 imbricated arrangement; other segments frequently ribbed, occasionally 

 cylindrical but more commonly subcuneate to reniform, the outer margin 

 entire, undulating or shallowly lobed, to 11mm long, 15 mm broad, and 

 averaging 0-75-1 -00 mm in thickness. 



Cortex of two to four layers of utricles with a fifth zone occasionally 

 present ; outermost utricles generally remaining attached after decalcification 

 for an average distance of 7 fxm, (26-)31-60 [xm in surface diameter, 

 30-60(-90) [i,m long in section, two or four supported by each secondary 

 utricle; secondary utricles 25-60(-78) (j.m broad, 28-70(-110) yun. long; 

 innermost utricles (34-)40-90 {inx broad. 



Nodal medullary filaments uniting as a single group for a distance of 

 approximately 25-55 yun, the adjacent filaments communicating by pores; 

 walls in this region thickened and pigmented. 



Type specimen. Puerto Rico, Culebra Island, Howe 4332, 

 6 March, 1906 (NY). 



