Acotyledon
Encyclopedia
Acotyledon is used to refer to seed plants or spermatophytes that lack cotyledon
s, such as orchids and dodder. Orchid seeds are tiny with underdeveloped embryos. They depend on mycorrhizal fungi for their early nutrition so are myco-heterotrophs
at that stage.
Although some authors, especially in the 19th century and earlier, use the word acotyledon to include plants which have no cotyledons because they lack seeds entirely (such as fern
s and moss
es), others restrict the term to plants which have seeds but no cotyledons.
Flowering plants or angiosperms are divided into two large groups. Monocotyledon
s or monocots have one seed lobe, which is often modified to absorb stored nutrients from the seed so never emerges from the seed or becomes photosynthetic. Dicotyledon
s or dicots have two cotyledons and often germinate to produce two leaf-like cotyledons. Conifers and other gymnosperm
s lack flowers but may have two or more cotyledons in the seedling.
Cotyledon
A cotyledon , is a significant part of the embryo within the seed of a plant. Upon germination, the cotyledon may become the embryonic first leaves of a seedling. The number of cotyledons present is one characteristic used by botanists to classify the flowering plants...
s, such as orchids and dodder. Orchid seeds are tiny with underdeveloped embryos. They depend on mycorrhizal fungi for their early nutrition so are myco-heterotrophs
Myco-heterotrophy
Myco-heterotrophy is a symbiotic relationship between certain kinds of plants and fungi, in which the plant gets all or part of its food from parasitism upon fungi rather than from photosynthesis. A myco-heterotroph is the parasitic plant partner in this relationship...
at that stage.
Although some authors, especially in the 19th century and earlier, use the word acotyledon to include plants which have no cotyledons because they lack seeds entirely (such as fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s and moss
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
es), others restrict the term to plants which have seeds but no cotyledons.
Flowering plants or angiosperms are divided into two large groups. Monocotyledon
Monocotyledon
Monocotyledons, also known as monocots, are one of two major groups of flowering plants that are traditionally recognized, the other being dicotyledons, or dicots. Monocot seedlings typically have one cotyledon , in contrast to the two cotyledons typical of dicots...
s or monocots have one seed lobe, which is often modified to absorb stored nutrients from the seed so never emerges from the seed or becomes photosynthetic. Dicotyledon
Dicotyledon
The dicotyledons, also known as dicots, are a group of flowering plants whose seed typically has two embryonic leaves or cotyledons. There are around 199,350 species within this group...
s or dicots have two cotyledons and often germinate to produce two leaf-like cotyledons. Conifers and other gymnosperm
Gymnosperm
The gymnosperms are a group of seed-bearing plants that includes conifers, cycads, Ginkgo, and Gnetales. The term "gymnosperm" comes from the Greek word gymnospermos , meaning "naked seeds", after the unenclosed condition of their seeds...
s lack flowers but may have two or more cotyledons in the seedling.