Wheldon : Key to the Harpidioid Hypna. 345 



30. Nerve 66 fi wide, median cells 66/1 long: plant short, yellowish, 

 irregularly divided, divisions subpinnate : alar cells yellow, incrassate, 

 obscure with granulations [D. pseudofluiians var. aqiiaiiciis i. dnnense). 

 Nerve stronger, very long, penetrating base of the long gradually attenuate 

 filiform acumen: plant slender and gracile, rather densely pinnate 

 above : 10-15 cm. [D. psendofluitans var. aqiiaticus f. tenuis). 



31. Leaves very distant, often laxly spreading below : stem elongate 

 (to 30 cm) with short distant branches, resembling in habit slender 



forms of var. paiernum (D. pseudofluitans var. aquaticus f. fluitans). 



Leaves closer, erect-secund below, more or less falcate above : shorter 

 (10-15 cm.), pinnate [D. pseudofluitans var. aquaticus). 



32. Robust to very robust : leaves erect patent, apical ones more 

 closely imbricate, finely but not longly acuminate (33). Slender and 

 ilexuose : leaves narrower, flexuose and lightly homotropous, prolonged 

 into a long fine twisted subule {D. pseudofluitans var. flexilis). 



33. Regularly pinnate, branches long or short : lower leaves lax 

 and sub-patent (35). Weaker, slender, simple or with few irregular 

 branches (34). 



34. Elongate : leaves very distant, narrower, ere^t flexuose, apical 

 convolute forming a secund cusp {D. pseudofluitans i. gracilis). Sub- 

 simple or irregularly divided, leaves more or less imbricate, so that 

 upper half of stems and branches are julaceous and pungent [D. pseudo- 

 fluitans f. acanthoclada) . 



35. Stems eflagellate, more or less regularly pinnate (D. pseudo- 

 fluitans var. paternum) . Stems pinnate below, ending above in a long 

 flagellate often branchless shoot, and also often bearing below numerous 

 long filiform distant-leaved innovations {D. pseudofluitans var. paternum 

 i. flagelliformis ) . 



36. Leaves acuminate subulate, acumen concave at base and usually 

 more or less falcate secund : alar cells distant from nerve (37). Leaves 

 not, or only slightly, falcate-secund, acumen plane : plant usually 

 more robust : alar cells less distinctly separated and sometimes reaching 

 to nerve (49). 



37. Leaves under 2 mm. long, rather brusquely acuminate from a 

 subdeltoid base (38). Leaves larger, 2-4 mm. long, more gradually 

 narrowed from an ovate to oblong-lanceolate base (42). 



38. Leaves falcate-secund,, not apiculate (39). Leaves subfalcate- 

 appressed, suddenly contracted into a straight fine apiculus : stems 

 filiform, fastigiately branched (6-8 cm.) : nerve 40 /< wide {D. aduncus 

 var. fllipolaris). 



39. Erect, rigid, short and slender, with many short pointed branches. 

 Leaves imbricate, lightly curved, points secund : nerved just beyond 

 mid-leaf : nerve 35 /< : lower third of leaf parenchymatous (D. aduncus 

 var. fllifonne) . Taller, also rigid, leaves more strongly falcate-secui^d 



40. Erect, 5-12 cm. high, nerved about half way (41). Depressed 

 interlaced and procumbent, more or less pinnate : nerve very short and 

 sometimes rudimentary, rarely reaching mid-leaf {D. aduncus var. 

 gracilescens f. tenue), 



41. Irregularly pinnately branched {D. aduncus var. gracilescens). 

 Densely fastigiately branched, branches slender (D. aduncus var. graci- 

 lescens f. fastigiata). 



42. Leaves erect -appressed, only lightly secund at the point : 

 apices of stems and branches only feebly curved (D. aduncus var. typicum 

 f. laevis). Leaves more or less strongly falcate-secund (43). 



43. Leaves strongly dimorphous : straight leaves erect flexiiose, 

 feebly curved, lanceolate, very longly subulate (3-4 mm.) : br. leaves 

 small (1-5-2 mm.), distinctly falcate-secund {D. aduncus var. Wheldoni 

 Dimorphism less marked, st. or br. leaves falcate-secund (44). 



44. Nerve strong (up to 53 fji) ; plant rather more robust (45). 

 Nerve weaker (47 /*) : plant more slender (46). 



1921 Oct. 1 



