Some familiar monoecious angiosperms are birch,
hazelnut, oak, pine, spruce, corn, and squash.
Monoecious also describes ancient plants, including
many mosses and algae, that lack flowers but
have both male and female reproductive organs
to produce spores. Monoecious species of all sorts
can be wind pollinated. The European ash has tiny
flowers that are either hermaphroditic or male and
depend on wind. Others lack apparent flowers but
have highly effective pollination schemes. In corn
(maize), the tassel atop the forming ear bears pollen.
Inconspicuous female flowers form rows along the
tiny cob and silks grow out from each ovary, ready
to receive pollen and direct it to the ovary. Once
fertilized, the rows become swelling kernels.
In self-pollinating species with perfect flowers,
male stamens may be aligned so that
pollen can simply fall onto the female
carpel that’s ready to convey its genes to
the ovule, where seed develops.
One way monoecious flowering plants
discourage self-fertilization is through
“self-incompatibility.” In these flowers,
if anthers and pistils mature at the
same time, structure and placement of
flowers can make it unlikely any pollen
will fertilize the same plant. More common
are flowers with an early season male (staminate)
phase, followed by a female phase. In still other
plant populations, early season whole flowers are
nearly all male, while more female flowers develop
later in the growing season.
And some plants undergo a sex change. In jack-
in-the-pulpit (Arisaema triphyllum), juvenile
plants produce all or mostly male flowers. As they
grow larger over the years, individuals have a
mix of both male and female flowers. The large
plants produce mostly female flowers.
Only about eight per cent of higher plant species
reproduce exclusively by non-sexual means, without
gametes. The next generation can sprout from
runners, from stems in contact with soil, or from
bulbs or bulb-like corms. And some produce viable
seeds without any fertilization at all.
“
ONLY ABOUT eight per
cent of higher plant
species reproduce
exclusively by non-sexual
means, without gametes.”
In case you were wondering, a so-called perfect
flower has both anthers that make pollen with
pistils ready to receive it. A perfect flower displays
a calyx of outer sepals, usually green, and a corolla
of inner petals. The sepals and petals together form
the perianth. Closer to the center, stamens produce
pollen grains, each containing a microscopic haploid
sex cell. The male parts of a flower collectively
form the androecium. Finally, in the middle, are the
carpels. At maturity, each holds one or more ovules
containing a tiny female gametophyte. The female
parts of a flower form the gynoecium.
grow cycle
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