102 
CERA TOPHYLL UM 
Exsiccata : — Billot, 3084; Fries ix, 64; Hansen, 1086; Welwitsch {FI. Lusit.), 801; Herb. FI. Ingric. 
vii, 236 B. 
Perennial. Stem up to nearly 1 m. long, lower nodes about as long as the leaves. Leaves 
rather rough, rigid, not collapsing when taken out of the water, about 1*5 cm. long, about 
8 in a whorl, branched, with 2 main segments, segments often more or less branched but less so 
than in C. submersum ; lobes subulate, broader than in C. submersum , margin spinulose, spinules 
rather more marked than in C. submersion. Flowers appearing in early July. Perianth of the 
staminate flowers about 4 mm. long and broad, cup purplish ; segments greenish and often dotted 
with purple, with 1 — 3 mucronations of various lengths at the tip. Stamens about 5—20, usually 
more numerous than in C. submersum , purplish. Perianth of the pistillate flowers about 1 mm. 
long and 2 high ; segments scarcely joined, paler than in the staminate flower. Stigmas 1 3, 
Map 40. Distribution of Ceratophyllum demersum in the British Islands 
long, projecting much beyond the perianth ; when 1, lateral. Achene ultimately black, with a 
terminal spine (the persistent remains of the stigma), sometimes with 2 lateral spines just below the 
apical one or with these subapical spines reduced to tubercles or absent, often with 2 lateral spines 
near the base, the sub-basal spines sometimes reduced to tubercles or quite absent, all the spines 
variable in length. 
{a) C. demersum var. apiculatum Ascherson FI. Brandenb. i, 219(1864); C. unicorne Dumortier Ft. belg. 
165 (1827); C. apiculatum Chamisso in Linnaea iv, 505, t. 5, fig. 6e (1829); C. demersum var. 7 Hooker and 
Arnott Brit. Ft. ed. 6, 371 (1850); C. demersum var. unicorne Rouy loc. cit. (1910); C. submersum var. apiculatum 
Dalla Torre und Sarnthein Farn- und Blutenpfl. Tirol 222 (1909). 
leones: — Smith Eng. Bot. t. 679, as C. submersum ; FI. Dan. t. 510, as C. submersum. 
Camb. Brit. FI. iii. Plate 98. {a, b) Fertile shoots, (c) Leaf (enlarged), (d) Ultimate lobe of leaf (en- 
larged). ( e ) Very young fruits (one enlarged), (f) Young fruits (one enlarged), (g) Ripening fruits (one 
