Mindblown: a blog about philosophy.
-
Size Range And Habitat
The ferns are extremely diverse in habitat, form, and reproductive methods. In size alone they range from minute filmy plants only 1–1.2 cm (0.39–0.47 inch) tall to huge tree ferns 10 to 25 metres (30 to 80 feet) in height. Some are twining and vinelike; others float on the surface of ponds. The majority of ferns inhabit warm, damp areas…
-
Introduction To Ferns
Fern, (class Polypodiopsida), class of nonflowering vascular plants that possess true roots, stems, and complex leaves and that reproduce by spores. The number of known extant fern species is about 10,500, but estimates have ranged as high as 15,000, the number varying because certain groups are as yet poorly studied and because new species are still being found in unexplored tropical areas. The ferns constitute an…
-
Appearance Of Gymnosperm Divisions
It is generally conceded that from the pteridosperms arose members of the division Cycadophyta. The first cycads appeared in the Permian Period (298.9 million to 252.2 million years ago), although fragmentary fossils of older age suggest that cycads were present during the preceding Carboniferous Period. Some of these presumed cycads differ from extant members in that megasporophylls were undivided, unlike those…
-
Earliest Gymnosperms
The earliest recognized group of gymnospermous seed plants are members of the extinct division Pteridospermophyta, known as pteridosperms or seed ferns. These plants originated in the Devonian Period and were widespread by the Carboniferous. In habit, seed ferns resembled some progymnosperms in that they were small trees with fernlike leaves (the equivalent of a progymnospermous flattened branch) bearing seeds.…
-
Evolution And Paleobotany
Gymnosperms were the first seed plants to have evolved. The earliest seedlike bodies are found in rocks of the Upper Devonian Series (about 382.7 million to 358.9 million years ago). During the course of the evolution of the seed habit, a number of morphological modifications were necessary. First, all seed plants are heterosporous, meaning that two kinds…
-
Gnetophyta
The division Gnetophyta has three families across three orders: Ephedraceae, Gnetaceae, and Welwitschiaceae. The family Ephedraceae consists of about 65 species of shrubs in a single genus, Ephedra. Gnetaceae has some 30 species in the genus Gnetum, many of which are trees or vines. Welwitschiaceae consists of a single species, Welwitschia mirabilis, characterized by a massive squat stem and two leaves. Some Ephedra species may have both microstrobili…
-
Ginkgophyta
The division Ginkgophyta consists of a single living species, Ginkgo biloba. A hardy deciduous tree, Ginkgo resembles an angiosperm in that the woody stem is frequently and irregularly branched and bears broad leaves, which are fan-shaped with dichotomously branched veins. Although it is now cultivated extensively around the world, Ginkgo is an endangered species, as its natural populations have been reduced to a small portion of the mountains…
-
Cycadophyta
Cycads resemble palm trees with fleshy stems and leathery featherlike leaves. The 10–11 genera and 305 living species are distributed throughout the world but are concentrated in equatorial regions. Cycads are typically short and squat, although the Australian cycad Macrozamia hopei may reach 19 metres (62 feet) in height. Given their attractive foliage and sometimes colourful cones, the…
-
Pinophyta
Known as conifers, members of the division Pinophyta are among the most diverse of the gymnosperms, with some 630 living species across six families. Some of the oldest living things on Earth are conifers, including several bristlecone pines (Pinus longaeva) found in the White Mountains of California that approach 5,000 years in age. Additionally, conifers are also the tallest and most-massive living…
-
Major Divisions
Scottish botanist Robert Brown first distinguished gymnosperms from angiosperms in 1825. While older classifications considered all seed plants to be assignable to a single division, Spermatophyta, more-recent classifications recognize that the characteristic of naked seeds is not important enough to be used to tie all plants with that feature into one group. Classification of gymnosperms now recognizes four extant divisions.
Got any book recommendations?