of the family Lemnaceae are the smallest flowering plants. They are
a distinct group of monocotyledonous plants. Not in without reason
they are called the most mysterious of the flowering plants on the Earth.
Because of their small sizes they sometimes remain elusive from casual
observation. The size of plants does not exceed 1 cm. Common
duckweeds (Lemna), greater duckweed (Spirodela), and water
meal (Wolffia) are frequently encountered by a number in one place.
Lemnaceae - aquatic, either freely floating or submerged (for example,
ivy leaf duckweed - Lemna
trisulca), larger partly long-standing (a structly tropical duckweed,
aequinoctialis, from Africa, is considered as the annual plant.
Lemnaceae - cosmopolitan plants (especially lesser duckweed, Lemna
minor), they extend throughout the entire world, with exception of
hot dry deserts and cold polar regions. About half of the 30 species
of this family dwell in the tropics and the subtropics, the rest - in the
temperate zone. The vegetative body of Lemnaceae according to the
form resembles the tiny floating sheet or the thallus of the lowest plants;
thus for long time they considered to be algae.
No unanimous opinion has been agreed for a word to designate the body
of these plants. Until now, since it has been called a fillokladiyem,
a vayey, a shield, a plate, a frond, a listets, a stem or a sheet.
In Russia, botanists more frequently is used the term of listets,
in foreign countries - fronds.
The fronds of Lemnaceae grow either singly or connected in small groups
or the networks by the short or elongated legs, formed by the narrow part
of the frond (transparent thread) (V.V.Petrov, 1991).
Green fronds of Lemna gibba and transparent
thread (waist of listetsa of white color).
Type of the right pocket of Lemna gibba.
The shapes of fronds are most diverse: reniform, rounded,
elliptical, lancet, linear, globular or oval. The vascular system
in Lemnaceae is practically absent, with exception of Spirodela,
in the roots of which there are tracheids. Roots are absent or are
weakly developed (Spirodela) and do not reach down to soil.
They are simple, with a root cap, on one or by beams emerging from
the abdominal surface of the fronds and fulfilling mainly functions of
anchors, which prevent the movement of plants in the water. The middle
part of the frods of Lemna and Spirodela is split by two
lateral pockets, in which are embedded the vegetative buds, from which
arise daughter fronds during vegetative multiplication. Sometimes
in one of the pockets a flower bud develops. In the representatives
of other species there is one pocket, and it serves exclusively for the
vegetative multiplication, whereas the flower bud is highly simplified:
to 1-2, rarely 3 (in Spirodela) one male and one female flower. A
perianth is absent (I.E.Ivanova, 1971). Male flowers consist of 1,
rarely 2 stamens with size/dimension near 1 mm. The measurement of
a stamen is a little more than 1 mm. Bilocular anthers are fastened
to the sealed threads and are supplied with conical pointed svyaznikom.
The ovary is egg-shaped, is monothecal, with 1-6 germs; post short and
thin/fine, and the stigma is extended in the form of shallow hopper or
cup with the uneven edges.
in the family of Lemnaceae is plotted not in what known for the flowering
plants rhythms, and it was observed so rarely which specially was recorded.
In Finland - are noted 33 cases of flowering from 1685-1947, in Poland
- only 2 times with 1679-1959, in America the flowering of Spirodela
in the last 200 years has been observed not more than 20 times.
In Armenia, according to the communication of A.L. Takhtadzhyana, in
1932 in the lakes of the Loriyakay highland plain they observed a mass
flowering of duckweed.
For the middle strip of Russia within the period from 1814 through 1978
in published reports appeared only about 25 findings of duckweed flowering.
In the ponds along the Volga river it was possible to observe the yearly
flowering of duckweed from 1972 through 1975 (A.L.Takhtadzhan, 1982).
In the Krasnodar edge during June 1995 in Krasnodare was noted an intensive
flowering of duckweed in Karasun lake and in the canals of the region of
Thapsyg Reservoir, during May 2000 (L.V. Tsatsenko, 2000).
It is possible that the flowering of Lemnaceae is not always noted by
botanists because of the microscopic dimensions of the flowers.
Duckweeds flower in the summer period, usually during June - August,
sometimes at the end of May or during September. At the beginning
of flowering more or less long chains separate into smaller groups, consisting
of 4-5 fronds in Lemna gibba and of 2-4 fronds in Lemna trisulca.
Before beginning flowering, morphological conversions of fronds occur gradually.
The air chambers increase in Lemna minor, fronds prepared for flowering
increase in the size, and acquire dark green pigmentation.
In Lemna trisulca vegetative fronds are thinned, become pale, and
its "top" is bent downward. In Lemna gibba flowering fronds
take on an olive- purple color (A.F.Pantyukh, 1986).
From the moment of the initiation of flowering fronds to the end of
the process of flowering pass about 20 days. For all Lemnaceae it
is characteristic protogonia, i.e.the stigma of the female flower
ripens first, then stamen of one of the male flowers, and after this the
stamen of the second flower. The process of the flowering of Lemnaceae
can be represented in the form of the following diagram:
| From the pocket of flowering fronds first appears
the stamen, which raises itself above the water. In the mouth of
stigma a large watery droplet of nectar then appears that apparently is
used for attracting small insects.
| With a touch, the droplet is pulled inside
the snout together with any pollen fallen on it. If dusting did not
occur, the drop appears again in several hours. The stigma
remains fertile over the course of twenty-four hours. Staurigamia
(cross pollination) occurs during this period.
| The stamens of the second male flower are advanced
from the pocket of flowering frond 24 h after the appearance of the first.
The anthers of the stamen of the first flower are closed until the moment
of the propagation of pollen, and stamen itself descends into the water
and it becomes transparent. The stigma is destroyed at this moment
and the pollen of the second flower can pollinate only adjacent flowering
| The stamens of the first flower function
about 60 h., the second - 90 h.
| In the beginning in the mature anthers is revealed
"entomophilous" brilliant yellow pollen, in the form of dense, moist clusters.
These clusters are torn off and fall on the surface of the green carpet
of water plants, on which small insects frequently warp (water bulb scale
mites, aphis). Dusting/pollination occurs with the aid of insects
|For 12-24 h after the anthers open, the pollen acquires
"anemophilic" appearance - it grows dim, it becomes faded and easily
friable. At this time it is transferred by airstreams over large
distances. Thus at first Lemnaceae are the
| If cross-pollination did not occur, then
self-fertilization can occur.
Fruits of duckweeds are well visible with the naked eye, according
to the sizes/dimensions they are just larger than a poppy seed.
of plants. Fruits of the family of Lemnaceae are transferred to the
large distances on the feet of the swimming and marshy birds. They
can also be transported by water. The predominates mode of reproduction
in Lemnaceae, however, is colonization by vegetative individuals, since
fruits are formed rarely. Adult plants spread via slowly flowing
water, by frogs and fish, to the bodies of which they stick, but predominantly
Many wild wild ducks eat Lemna and Spirodela. They
can stick to the paws of birds and are thuy transferred over large distances.