DUCKWEED FAMILY 93 
Order IIL.—HELOBIAE. Water Plants 
While all the plants of this order are fluvial the order does not 
by any means include all aquatic plants. 
The flowers may be destitute of floral envelopes or may have 
very imperfect perianths, or have perfectly developed and showy 
flowers, as in the Sagittaria. The stamens vary from one to many, 
the pistils also are indefinite in number. 
The characteristics of plants included in this order are therefore 
so varied that they must be found in the characteristics of the 
different families. 
SYNOPSIS OF THE FAMILIES OF THE ORDER HELOBIAE 
- Small rounded green bodies floating on the surface of pools 
. LEMNACEAE 
Plants Pibmevsed 6 or aoenan “nei se inconspicuous green- 
ish flowers. Submersed plants with upper leaves some- 
times floating, lower leaves alternate. Flowers situated 
on a fleshy cylinder, in a small axillary group or on a 
grooved receptacle, perianth wanting or consisting of 4 
fleshy segments. Leaves sheathing at base. Flowers in 
axils of oe ve flowers with double perianth 
- . . NATADACEAE 
Pinte with ae im thee ae with aerial stems and more 
or less conspicuous flowers. Perianth segments 6; sta- 
mens 6. Marsh plants with half-rounded, deeply-grooved 
leaves with membraneous sheaths at the base, not en- 
tirely submersed, flowers in Moe spikes terminally on tall 
flower stems . . . . Ree TRIGLOCHINEAE 
Marsh herbs commonly not aici submersed, but usually 
growing in water, with sheathing leaves, with flowers on 
a tall aerial spike and with the perianth (calyx and co- 
Bola) aie F's. yy!) 9s See 4 on. 2, AESMACEAR 
Submersed herbs with ee arising from a spadix (a fleshy 
cylinder), but not surrounded by or resting upon a spathe 
(a leaf-like envelope) . . .°. . VALLISNERIACEAE 
Famity I.—LEMNACEAE. DucKweep FAMILY. 
Minute swimming plants, small green scales floating on the sur- 
face of still pools. The vegetative apparatus is reduced to a small 
