(254) Ceratophyllum - leaves whorled, 2-3 times furcately dissected.
(255) Callitriche - leaves opposite, entire.
(257) Parietaria - perianth of female flowers four-cleft; stamens four.
(258) Hunmlus - perianth of female flowers a mere scale; stamens five.
(259) Rumex - perianth six-parted, the three inner segments becoming enlarged. (2G0) Oxyria - perianth four-parted, the two inner segments enlarged.
(261) Polygonum - perianth five-parted, the segments nearly equal.
(262) Thesium - leaves alternate, entire, without stipules.
(263) Euphorbia - flowers collected in heads, surrounded by a 4-5-toothed perianth-like involucre, enclosing several male flowers (each a single stamen, with jointed filament), and one female (a solitary three-celled stalked ovary). (264-) Mercurialis - herbs, with the male and female flowers separate, dioecious or monoecious.
(265) Aristolochia - perianth tubular, very oblique; stameus six.
(266) Paris - perianth of 8-10 narrow, spreading or reflexed segments.
(267) Tamus - perianth of six segments.
(269) Typha - spadix (flower spike) cylindrical.
(270) Sparganium - spadix spherical.
(271) Lemna - flowers monoecious; spathe urceolate; stamens 1-2.
(272) Potamogeton - flowers perfect, in pedunculated spikes or heads.
(273) Zannichellia - flowers monoecious, axillary and sessile.
(274) Stratiotes - stem scarcely any; leaves sword-shaped, tufted, radical, submerged; flowers polyandrous.
(275) Hydrocharis - stem root-like, bearing tufts of roundish floating leaves; flowers 9-12-androus.
(276) Anacharis - stems submerged, branched, with small opposite or whorled leaves; flowers minute, with nine stamens, or three styles.
(277) Iris - perianth six-leaved, the three outer larger; stigmas three, petal-like, arching over the stamens.
(278) Gladiolus - perianth six-leaved, the divisions similar, with a somewhat oblique two-lipped arrangement, 68. Orchidaceous Plants. Orchidaceae.
* Anther single, the pollen simple, or consisting of granules in a slight state of cohesion.
(279) Listera - perianth ringent; lip deflexed, linear, or oblong, two-lobed; anther parallel with the stigma, enclosed in a hood.
(280) Epipactis - perianth patent; lip interrupted, the basal division concave, terminal one larger, with two projecting plates at its base above; anther terminal.
(281) Cephalanthera - perianth converging; lip interrupted, the basal division saccate, jointed to the recurved terminal one, which is without protuberances at the base; anther terminal.
** Anther single, the pollen cohering in grains or masses, which are indefinite in number and ivaxy.
‡ Lip spurred.
(282) Orchis - perianth ringent, hooded; lip three-lobed; pollenmasses with two glands enclosed in a common pouch; anther-cells converging at the base.
(283) Gymnadenia - as in Orchis, but the glands of the pollenmasses naked (without a pouch); anther-cells parallel at the base.
(284) Habenaria - perianth ringent, hooded; lip three-lobed or entire; glands of the stalks of the pollen-masses naked; anther-cells diverging at the base.
‡‡ Lip not spurred.
(285) Aceras - as in Orchis, except that the spur is wanting.