CERA TOPHYLLUM 
IOI 
the statement that de Jussieu referred Ceratophyllum to the Monocotyledones is scarcely correct: he refers them ( Gen. PI. 18 
(1789)) to his “order” Naiades , a heterogeneous group containing, among other genera, Hippuris and Myriophyllum ; and 
the “order” is placed in his Acotyledones, and not in his Monocotyledones. 
A good account of the genus is to be found in von Martius’ FI. Brasil, vol. iii, pt. iii (1894). 
About 3 — 6 species ; cosmopolitan. 
British species of Ceratophyllum 
1. C. submersum (see below). Leaves smoother, longer, less rigid, more divided, and less 
tufted at the ends of the branches than in C. demersum. Style shorter. Achene with a shorter 
terminal spine and no lateral spines. 
2. C. demersum (see below). Leaves rougher, shorter, stiffer, less divided, and usually more 
tufted at the ends of the branches than in C. submersum. Style longer. Achene with a longer 
terminal spine, often with 2 (rarely more) lateral spines also. 
I. CERATOPHYLLUM SUBMERSUM. Hornwort. Plate 97 
Hydroceratophyllum folio laevi octo cornibus armato Dillenius in Ray Syn. ed. 3, 135 (1724). 
Ceratophyllum submersum L. Sp. PI. ed. 2, 1409 (1763); Smith Ft. Brit. 1020 (1804) partim 1 ; 
Nolte Nov. FI. Holsat. 77 (1828); Rouy et Foucaud FI. France 
xii, 280 (1912); C. demersum var. /3 L. Sp. PI. 992 ( 1 753) » C- 
muticum Chamisso in Linnaea iv, 505 (1829); v, 336, t. 4, fig. A 
et B (1830); C. vulgare var. muticum Schleiden in Linnaea xi, 541, 
t. 11, fig. 16 (1837) partim 1 ; C. aquaticum subsp. submersum Syme 
Eng. Bot. viii, 124 (1868) ; C. demersum var. submersum von Martius 
FI. Brasil, iii, pt. 3, t. 125, fig. f (1894). 
leones : — Camb. Brit. FI. iii. Plate 97. (a) Fertile shoot. 
(b) Leaf. ( c ) Ultimate lobe of leaf (enlarged), (d, e,f) Ripening 
fruits (enlarged), (g, h ) Fruits (enlarged). Kent (M. W.). 
Exsiccata : — Billot, 1192; Fries, ix, 63 ; Reichenbach, 1419; 
Schultz (H. N.), i, 49. 
Closely allied to C. demersum var. apiculatum , but 
differing from that variety in the following characters : — 
Shoot paler green, less rough, less rigid, leaflets col- 
lapsing when taken out of the water. Leaves longer 
(up to about 5 cm.), smoother, divided into more numerous slender and longer lobes, lobes less 
markedly spinulose. Flowers July to September. Stamens often only 4 — 6. Style shorter. Achene 
smooth and whitish when young ; when mature, often more or less covered with small acute and 
rather distant tubercles except on the slightly winged margins ; terminal spine very short and merely 
mucronoid, lateral spines absent. 
Local, in stagnant and brackish waters in southern and eastern England ; Somerset, and from 
Sussex to Lincolnshire ; locally abundant in the ditches bordering the estuary of the Thames in 
northern Kent. Records for central England and Scotland require verification, owing to confusion 
with C. demersum var. apiculatum , though it is quite possible the species has a wider distribution 
than we here allow. Not recorded for Wales or Ireland. 
Recorded for Sweden, Denmark, Germany, Holland, Belgium, France, central Europe, Russia, 
southern Europe ; northern Africa ; Asia. Doubtless some of these places only furnish C. demer- 
sum var. apiculatum (cf. p. 102). 
2. CERATOPHYLLUM DEMERSUM. Hornwort. Plates 98, 99 
Millefolium aquaticum cornutum Ray Cat. Angl. 210 (1670); M. aquaticum equisetifolium seu aquaticum 
ramosum aquis immersum Ray Syn. ed. 2, 280 (1696); Hydroceratophyllum folio aspero quatuor cornibus armato 
Ray Syn. ed. 3, 135 (1724). 
Ceratophyllum demersum L. Sp. PI. 992 (1753) excl. var. /3; ed. 2, 1409 (1763); Smith FI. Brit. 
1020 (1804); Rouy FI. France xii, 281 (1910). 
leones: — Von Martius FI. Brasil, t. 125, excl. fig. / (several varieties). 
1 Many botanists have confused under one name the two plants C. submersum and C. demersum var. apiculatum. 
Map 39. Distribution of C. submersum in England 
