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In addition to animals, the flowers of some plants also show bilateral symmetry. Such plants are referred to as zygomorphic and include the orchid (Orchidaceae) and pea families, and most of the figwort family (Scrophulariaceae). [18] [19] The leaves of plants also commonly show approximate bilateral symmetry.
Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts. Uncommonly, flowers may have no axis of symmetry at all, typically because their parts are spirally arranged.
A Phalaenopsis flower. Orchids are easily distinguished from other plants, as they share some very evident derived characteristics or synapomorphies.Among these are: bilateral symmetry of the flower (zygomorphism), many resupinate flowers, a nearly always highly modified petal (labellum), fused stamens and carpels, and extremely small seeds.
Within the monocotyledons, plants belonging to the Amaryllidaceae family have the simplest and most typical flowers. The flowers are hermaphrodites, actinomorphics (i.e., of radial symmetry) or slightly zygomorphics, pedicellate or sessiles, showy, each associated with a filiform bract.
Animals mainly have bilateral or mirror symmetry, as do the leaves of plants and some flowers such as orchids. [30] Plants often have radial or rotational symmetry, as do many flowers and some groups of animals such as sea anemones. Fivefold symmetry is found in the echinoderms, the group that includes starfish, sea urchins, and sea lilies. [31]
A normal (left) and a peloric Streptocarpus showing the bilateral to radial symmetry alteration.. Pelorism has been of interest since a five-spurred variety of the common toad-flax (Linaria vulgaris L.) was first discovered in 1742 by a young Uppsala botanist on an island in the Stockholm archipelago and then in 1744 described by Carl Linnaeus.
A gynandromorph can have bilateral symmetry—one side female and one side male. [24] Alternatively, the distribution of male and female tissue can be more haphazard. Bilateral gynandromorphy arises very early in development, typically when the organism has between 8 and 64 cells. [25] Later stages produce a more random pattern. [citation needed]
To the contrary, plants in the Mimosoideae subfamily of legumes have the petals reduced, and have numerous stamens arranged in showy spikes. In the Caesalpinioideae subfamily of legumes the upper petal is initially enveloped by the lateral petals, before the petals unfold to assume a radial five-fold symmetry. [9]