Aquatic herbs. Leaves with axillary scales. Flowers solitary or spicate, regular, with 1-4-merous whorls. Perianth simple and little developed or wanting. Stamens 1-4. Anthers sessile, opening outwards or laterally. Carpel 1, with a 1-celled ovary, or several distinct or almost distinct carpels. Ovules solitary in each carpel, very rarely 2, pendulous or laterally fixed Fruit indehiscent. Seed exalbuminous. Embryo with a strongly developed radicle.—Genera 8, species 35. (Including ZOSTERACEAE, under NAIADACEAE.) (Plate 4.)

1. Flowers in spikes, hermaphrodite or polygamous, without a perianth, but the stamens sometimes provided with a sepal-like connective. 2
Flowers solitary or in cymes, unisexual. 5
2. Spikes with a flat axis, at the time of flowering enclosed in the sheaths of the uppermost leaves. Stamen 1. Pollen-grains filiform. Carpel
1. Stigmas 2, on a short style. Embryo with a very large radicle and a tail-like cotyledon. Submerged marine plants.—Species 2. North and
South Africa and Madagascar. Used for stuffing and as packing material.
“Grass-wrack.” [Tribe ZOSTEREAE.] Zostera L.
Spikes with a cylindrical axis, at the time of flowering not enclosed in the sheaths of the uppermost leaves. Stamens 2-4. Stigma 1, undivided
or many-parted. 3
3. Spikes compound, submerged. Spikelets shorter than their bracts. Flowers polygamous. Stamens 3, rarely 4. Pollen-grains filiform. Carpel 1.
Stigma divided (or provided with narrow appendages). Embryo with
a very large radicle and a straight cotyledon resembling the leaves of the plumule. Marine plants.—Species 1. Mediterranean Sea. The leaves are used for packing and thatching, and also in medicine. [Tribe
POSIDONIEAE.] Posidonia Koen.
Spikes simple, above the water. Flowers hermaphrodite. Pollen-grains globular or bent. Carpels usually 4. Stigma simple, more or less peltate. Embryo with a curved cotyledon. [Tribe POTAMOGETONEAE.] 4
4. Spikes two-flowered. Stamens 2. Anthers with a very short appendage and kidney-shaped cells opening outwards. Pollen-grains bent. Fruit stalked. Embryo with a very thick radicle. Salt-water plants. Leaves subulate.—Species 1. Ruppia L.
Spikes several-flowered. Stamens 4. Anthers with a sepal-like appendage and straight cells opening laterally. Pollen-grains globular. Fruit sessile. Embryo with a slightly thickened radicle.—Species 20. Used for manure; some have edible root-stocks. “Pondweed.” (Plate 4.) Potamogeton Tourn.
5. Perianth none. Stamens 2. Pollen-grains filiform. Carpels 2. Stigmas strap-shaped, longer than the style. Embryo with an accumbent cotyledon. Marine plants. [Tribe CYMODOCEAE.] 6
Perianth present, at least in the female flowers. Stamens 1-2. Pollen-grains globular. Carpels 3-9. Stigma shield- or funnel-shaped, shorter than the style. Embryo with a hooked or rolled cotyledon.
Fresh- or brackish-water plants. [Tribe ZANICHELLIEAE.] 7
6. Stigma 1. Anthers inserted at slightly different heights. Ripe carpels scarcely compressed.—Species 2. Indian Ocean, Red Sea, Angola.
(Halodule Endl., under Cymodocea Koen.) Diplanthera Thouars
Stigmas 2. Anthers inserted at the same height. Ripe carpels compressed and keeled.—Species 5. North Africa, Senegambia, East Africa,
Madagascar and neighbouring islands. (Including Phycagrostis Ascherson) Cymodocea Koen.
7. Perianth in the male flowers none, in the female cup-shaped and undivided.
Anthers stalked, opening by 2 longitudinal slits. Carpels usually 4, slightly curved, with a peltate stigma.—Species 1. North and South
Africa, southern West Africa, Madagascar and neighbouring islands. Zannichellia Mich.
Perianth in the male flowers 3-toothed, in the female consisting of 1-3 segments. Anthers sessile, opening with one longitudinal slit. Carpels
3, straight, with a funnel-shaped stigma.—Species 1. North-west
Africa (Algeria). Althenia Fr. Petit

APONOGETONACEAE.

FLOW. PL. AFR. Pl. 5.

J. Fleischmann del.

Aponogeton leptostachyus E. Mey.

A Plant in flower. B Female flower. C Carpel cut lengthwise.

ALISMATACEAE