Flowering plants are technically known as angiosperms, which means enclosed or covered seeds. All flowering plants produce fruits with enclosed seeds. This method of reproduction has allowed flowering plants to become the dominant plants of earth's flora. Botanists estimate that there are 260,000 species of flowering plants, which comprise 88 per cent of the species in the plant kingdom. Botanists consider angiosperms the most advanced plants on earth.
Cotyledons are the parts of flowering plants that store food in seeds. They closely resemble leaves and are the first part of the plant to emerge from a seed. Cotyledons provide nutrients to the seedling until it can begin photosynthesis. The appropriate time to transplant a seedling is when the first of its "true leaves" appear above or between the cotyledons, the University of Maryland Extension says.
Monocots and Dicots
Angiosperms are divided into two major classes: monocots and dicots. "Mono" means "one," and monocot means the embryo has one cotyledon. Monocots include grasses, irises, lilies, tulips, onions and garlic. "Di" means "two," and dicot means the embryo has two cotyledons. Dicots include roses, rhubarb and hydrangea.
A plant's eggs, or ovules, contain endosperm, a tissue that grows after the ovule is fertilised to provide the plant's embryo with nutrients while it is in its seed. Cotyledons can absorb endosperm while seeds are developing. Seeds of some species keep their nutrients primarily in the endosperm, having very small cotyledons; others store most of their nutrients in cotyledons and their endosperm is quite small.
In many dicots, the cotyledons not only transfer nutrients to the developing plant but also turn green and produce more food through photosynthesis until they fall off. The two cotyledons also protect the seedling's stem and first leaves from physical injury. Wheat, corn and grain sorghum are grassy crops, which are monocots. For grassy crops, the cotyledon plays a protective role underground as a shield for the emerging shoot, while the endosperm provides the nutrient source for germination and early seedling development.
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- University of Maryland College of Computer, Mathematical and Natural Sciences; BSCI 124 Lecture 20 -- Flowering Plants; 1998
- University of Illinois Extension; Great Plant Escape Glossary; Cotyledon
- University of Maryland Extension; Grow It Eat it; Potting Up; March 2011
- University of California Museum of Paleontology: Monocots Versus Dicots: The Two Classes of Flowering Plants
- North Carolina State University; BIO 183 Laboratory
- University of Cincinnati Clermont College; Department of Biology; Angiosperms; J. Stein Carter; 2004