In biological taxonomy, division is a rank that is used differently in zoology and in botany.
In botany and mycology, division is the traditional name for a rank now considered equivalent to phylum. The use of either term is allowed under the International Code of Botanical Nomenclature.
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In fungi, an ascospore is the sexual spore formed inside an ascus—the sac-like cell that defines the division Ascomycota, the largest and most diverse division of fungi. After two parental nuclei fuse, the ascus undergoes meiosis (halving of genetic material) followed by a mitosis (cell division), ordinarily producing eight genetically distinct haploid spores; most yeasts stop at four ascospores, whereas some moulds carry out extra post-meiotic divisions to yield dozens. Many asci build internal pressure and shoot their spores clear of the calm thin layer of still air enveloping the fruit body, whereas subterranean truffles depend on animals for dispersal.
Development shapes both form and endurance of ascospores. A hook-shaped crozier aligns the paired nuclei; a double-membrane system then parcels each daughter nucleus, and successive wall layers of β-glucan, chitosan and lineage-specific armour envelop the incipient spores. The finished walls—smooth, ridged, spiny or gelatinous, and coloured from hyaline to jet-black—let certain ascospores survive pasteurisation, deep-freezing, desiccation and ultraviolet radiation. Dormant spores can lie inert for years until heat shock, seasonal wetting or other cues trigger germ tube emergence. Such structural and developmental traits are mainstays of fungal taxonomy and phylogenetic inference.
Chlorophyta is a division of green algae informally called chlorophytes.
Pteridospermatophyta, also called pteridosperms or seed ferns, are a polyphyletic grouping of extinct seed-producing plants. The earliest fossil evidence for plants of this type are the lyginopterids of late Devonian age. They flourished particularly during the Carboniferous and Permian periods. Pteridosperms declined during the Mesozoic Era and had mostly disappeared by the end of the Cretaceous Period, though Komlopteris seem to have survived into Eocene times, based on fossil finds in Tasmania.
With regard to the enduring utility of this division, many palaeobotanists still use the pteridosperm grouping in an informal sense to refer to the seed plants that are not angiosperms, coniferoids (conifers or cordaites), ginkgophytes (ginkgos or czekanowskiales), cycadophytes (cycads or bennettites), or gnetophytes. This is particularly useful for extinct seed plant groups whose systematic relationships remain speculative, as they can be classified as pteridosperms with no invalid implications being made as to their systematic affinities. Also, from a purely curatorial perspective the term pteridosperms is a useful shorthand for describing the fern-like fronds that were probably produced by seed plants, which are commonly found in many Palaeozoic and Mesozoic fossil floras.
The zosterophylls are a group of extinct land plants that first appeared in the Silurian period. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zosterophyllophyta or Zosterophyta and the class or plesion Zosterophyllopsida or Zosteropsida. They were among the first vascular plants in the fossil record, and had a world-wide distribution. They were probably stem-group lycophytes, forming a sister group to the ancestors of the living lycophytes. By the late Silurian (late Ludlovian, about 420 million years ago) a diverse assemblage of species existed, examples of which have been found fossilised in what is now Bathurst Island in Arctic Canada.