POND-WEED TRIBE 27 
lanceolate, narrowing at the top, and tipped with a short spine; stipules 
large and winged; spike dense, many-flowered. This is a handsome Pond- 
weed. Its large clear olive-green membranous leaves have wavy edges, and 
‘are beautifully veined. It is the largest of our native species, and forms 
masses in ponds, ditches, and rivers, where it is often abundant. We have, 
however, no species like the P. serratum of the Swiss lakes, which Haller 
describes as growing to the enormous length of from ten to twenty fathoms, 
forming a kind of forest in their waters. Our Shining Pond-weed bears 
cylindrical spikes of green flowers, about two inches long, in June and July. 
Two sub-species are recognised: P. zizii and P. decipiens. The former has 
oblong floating leaves, somewhat leathery, and a very long stalk to the 
flowering spike ; the latter has variable stalkless leaves, a denser spike on a 
stouter stalk. 
15. Small Pond-weed (P. pusillus).—Leaves linear, acute, 1 to 3-ribbed, 
alternate, spreading at the base ; stem thread-like, branched ; spikes on very 
long stalks. This species is not infrequent in rivers, ponds, and ditches in 
July, when it bears its nearly globular few-flowered spikes of brownish-green. 
Its leaves are usually very narrow, and expanded at the base, of a dull green. 
A variety with broader leaves and compressed stem is the Flat-stalked Pond- 
weed (P. friesiz) of some writers. 
16. Hair-leaved Pond-weed (P. trichoides).—Stem hair-like ; leaves 
bristle-like, rigid, with half-clasping base, 1 to 3-nerved, stipules slender and 
sharp; flowers 3 to 6, very minute, only one producing fruit; flower-stalk 
curved, longer than the leaves. This slender species, nevertheless, attains a 
length of six or eight feet. It occurs in muddy drains and ditches in Nor- 
folk, Suffolk, and Cambridge ; also in the west of Ireland. It flowers from 
August to October. 
17. Grassy Pond-weed (P. graméneus).—Leaves linear, broad, alternate, 
sessile ; stem compressed, forked; flower-stalks scarcely longer than the 
spikes or the stipule. This is a somewhat rare plant, inhabiting ponds and 
ditches, bearing a dense egg-shaped spike in July. Its leaves are of a full 
deep though bright green, with three nerves, and look like grass as they float 
on the water. It is also known as P. obtuszfolius. 
18. Sharp-leaved Pond-weed (P. acutifdlius).—Leaves linear, taper, 
pointed, oval, compact, with three strong and numerous fine nerves, and 
half clasping the stem. This rare species has been found in lakes and ditches 
from Yorkshire to Dorset and Kent. It flowers in July. 
19. Grass-wrack-like Pond-weed (P. zosterefdlius).—Leaves broadly 
linear, acute, with 3, rarely 5, strong and many fine nerves; spikes many- 
flowered, one inch long, cylindrical, upon long foot-stalks. This is a local 
plant, inhabiting rivers and lakes in the north and east of Britain, and in 
County Down. It flowers in July, and is larger than the last species. It is 
also known as P. compressus. 
* * * Leaves all submersed, without stipules. 
20. Close-leaved Pond-weed (P. dénsus).—Leaves opposite, egy- 
shaped, tapering to a point; stem forked; spikes 3 to 6-flowered. This 
species is rendered of easy recognition by its pellucid crowded leaves, which 
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