Search results
Results from the WOW.Com Content Network
The gymnosperms (/ ˈ dʒ ɪ m n ə ˌ s p ɜːr m z,-n oʊ-/ ⓘ JIM-nə-spurmz, -noh-; lit. ' revealed seeds ') are a group of woody, perennial seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include conifers, cycads, Ginkgo, and gnetophytes, forming the clade Gymnospermae [2] The term gymnosperm comes from the ...
Some gymnosperms bear needles with only one vein, but these evolved later from plants with complex leaves. [1] An interesting case is that of Psilotum, which has a (simple) protostele, and enations devoid of vascular tissue. Some species of Psilotum have a single vascular trace that terminates at the base of the enations. [2]
Vascular cambia are found in all seed plants except for five angiosperm lineages which have independently lost it; Nymphaeales, Ceratophyllum, Nelumbo, Podostemaceae, and monocots. [1] In dicot and gymnosperm trees, the vascular cambium is the obvious line separating the bark and wood; they also have a cork cambium.
If they do have secondary growth, it differs from the typical pattern of other seed plants. The formation of secondary vascular tissues from the cambium is a characteristic feature of dicotyledons and gymnosperms. In certain monocots, the vascular tissues are also increased after the primary growth is completed but the cambium of these plants ...
The presence of vessels in xylem has been considered to be one of the key innovations that led to the success of the flowering plants. It was once thought that vessel elements were an evolutionary innovation of flowering plants, but their absence from some basal angiosperms and their presence in some members of the Gnetales suggest that this hypothesis must be re-examined; vessel elements in ...
Botanists define vascular plants by three primary characteristics: Vascular plants have vascular tissues which distribute resources through the plant. Two kinds of vascular tissue occur in plants: xylem and phloem. Phloem and xylem are closely associated with one another and are typically located immediately adjacent to each other in the plant.
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue: the vascular cambium and the cork cambium.
However, molecular studies (and some more recent morphological [7] [8] and fossil [9] papers) have generally shown a clade of gymnosperms, with the gnetophytes in or near the conifers. For example, one common proposed set of relationships is known as the gne-pine hypothesis and looks like: [10] [11] [12]