i6 



BRITISH FLORA 



shaped, obliquely ovoid, flattened, with an obscure 

 keel, with a straight inner edge, with a tooth near 

 the base, warted on the back, with a tubercle at 

 the base when fresh, and with a short beak. The 

 plant is in flower in July and August, and is a 

 herbaceous perennial. 



Fennel -leaved Pondweed (Potamogeton pecti- 

 nalus, L. = P. marinus, Huds.). The habitat of 

 this plant is fresh and brackish ditches, streams, 

 and ponds. The stem is slender, branched, densely 

 branched, forming a thick flat mass. The root is 

 a thick tuber. The leaves are long, linear, made 

 up of 2 interrupted tubes, with a long narrow 

 point, the upper leaves bristle-like, 1-3 ribbed, the 

 lower flattened, 5-nerved. The stipules form a 

 sheath with a free tip. The flowers are in an 

 interrupted whorl, few, and distant. The stalks 

 are long and slender, not thickened above. The 

 fruit is large, swollen, broadly half-inversely ovate, 

 the inner edge convex, rounded on the back, with- 

 out ridges. The nut has 2 strong lateral ridges, 

 and is not keeled, but has a short beak. The 

 plant flowers in July and August, and is a herb- 

 aceous perennial. 



Potamogeton vaginafus, Turcz. This species is 

 regarded as a variety of the last, found in Shet- 

 land. 



Potamogeton flabellatus, Bab. ( = P. interruptus, 

 Kit.). The habitat of this species is streams, ponds, 

 and ditches, chiefly near the sea. The stem is, 

 when floating, long, branched, wavy, fanlike 

 (hence flabellatus). The rhizome is spreading 

 from a tuber. The lower leaves are broadly 

 linear, flat, with an abrupt apiculus, or long narrow 

 point, 3~5-veined, the veins transverse, distant 

 from the margin. The upper leaves are narrow, 

 acute, i-3-veined, the lateral veins marginal. The 

 flowers are in interrupted spikes. The fruit is 

 broadly half-inversely ovoid, the inner edge more 

 or less straight, the lateral ribs not well-marked, 

 and not ribbed on the back when fresh, but rounded. 

 There is a prominent keel on the nut. The plant 

 flowers in July and August, and is a herbaceous 

 perennial. 



Fine-leaved Pondweed (Potamogeton filiformis, 

 Nolle = P. martnus, L.). This plant is found in 

 lakes and ditches. The stem is slender (hence 

 filiformis), branched below, simple above, with 

 short branches. The leaves are like those of P. 

 pectinatus, but longer. They are linear, bristle- 

 like, i -nerved, the veins transverse, channelled, 

 alternate. The flowers are in a much-interrupted 

 spike, in dense whorls, with very slender stalks, 

 longer than the leaves. The drupelets are hardly 

 keeled, inversely ovate, rough, rounded dorsally 

 when dry. The nut is round on the back, with a 

 very short, terminal beak. The plant flowers from 

 July to September, and is a herbaceous perennial. 



Horned Pondweed (Za nn ichellia palustris, L.). 

 The habitat of this plant is fresh and brackish 

 waters, pools, ditches, ponds, and streams, stag- 

 nant water. The plant is floating or submerged, 

 and has the pondweed habit. The stems are 

 thread-like or bristle-like, with spreading branches. 

 The leaves are opposite or in whorls, slender. 



The flowers are without stalks, in the axils. The 

 achencs are curved, with a smooth keel, stalkless. 

 There are i or 2 stamens in the male flowers, 

 which are long-stalked. The females consist of 

 i free or shortly-stalked carpel, in groups of four 

 or less, with a cup-like spathe, which may be en- 

 tire. The plant flowers from May to August, and 

 is a herbaceous annual. 



Zannichellia polycarpa, Nolle. The habitat of 

 this species is brackish water. The leaves are 

 opposite, thread-like. The anthers are 2-celled, 

 the anther-stalks very short. The stigma is large 

 and wavy on the margin. The style is very short. 

 The achenes are 5-6, more or less stalkless. The 

 nuts are close together, crenulate on the back. 

 The plant flowers between May and August, and 

 is a herbaceous annual. 



Naias flexilis, Rostkov & Schmidt. The habi- 

 tat of this plant is deep lakes. The stem is 

 branched, brittle, slender. The leaves are very 

 slender, narrow, ternate, 3 in a whorl, or opposite, 

 transparent, with very small distant teeth, or 

 entire, veined. The sheaths are fringed with 

 hairs, or have very small teeth. The flowers are 

 solitary or 2-3. The anther is i-locular. The 

 style is short. The ovary is solitary, stalkless, 

 in the axils. The plant is floating, flowering in 

 August and September, and is a herbaceous per- 

 ennial. 



Naias marina^ L. ( = N. major, All.). This is a 

 very rare plant. The stems are repeatedly forked 

 into 2 branches from near the base, with a few 

 teeth. The leaves are opposite, or in whorls of 3, 

 linear, with numerous, large, spinous teeth, the 

 back and upper internodes also bearing spines, 

 and with coarse teeth. The sheaths are round 

 and more or less entire. The flowers are solitary. 

 The male flower is enclosed in a spathe. The 

 anther is 4-locular. The drupe is ellipsoid or 

 ovoid, purplish, succulent, and narrowed above 

 into a stout style which does not fall. The plant 

 is 3-9 in. in height, flowering in July, and is a 

 herbaceous perennial. 



Naias gramineOi Del. This has been introduced 

 into Britain in a canal at Reddish, Lancashire, in 

 Egyptian cotton, from a mill which pours out waste 

 hot water. The stem is branched throughout, 

 with numerous, simple, lateral branches. The 

 leaves are tufted, narrow, linear, with many 

 small, spinous teeth. The sheaths are toothed 

 and auricled. The male flowers are stalked, with 

 4-locular anthers. There are 2 stigmas. The 

 fruit is either solitary or in groups of 2-4, and is 

 narrowly ellipsoid. The plant is floating, flower- 

 ing between July and September, and is a herb- 

 aceous annual. 



ORDER CYPERACE/E 



Brown Cyperus (Cyperus fuscvs, L.). The 

 habitat of this plant is ditches and wet meadows, 

 shallow water. The plant has the sedge habit. 

 The stems are numerous, 3-sided, from a fibrous 

 root, which is tufted. The plant is nearly prostr- 

 ate. The leaves are grass-like, spreading, flat. 



