Isostylis
| Banksia subg. Isostylis | |
|---|---|
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| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| Order: | Proteales |
| Family: | Proteaceae |
| Genus: | Banksia |
| Subgenus: |
B. subg. Isostylis R.Br. |
| Species | |
Banksia subg. Isostylis is a subgenus of Banksia. It contains three closely related species, all of which occur only in Southwest Western Australia. Members of subgenus Isostylis have dome-shaped flower heads that are superficially similar to those of B. ser. Dryandra, but structurally more like reduced versions of the "flower spikes" characteristic of most other Banksia taxa.
There are three species of Banksia subg. Isostylis, B. ilicifolia (Holly-leaved Banksia), B. cuneata (Matchstick Banksia) and B. oligantha (Wagin Banksia). B. ilicifolia is widely distributed and relatively common, but the other two species are rare and threatened.
B. subg. Isostylis shares with B. ser. Dryandra the property of having compact, dome-shaped flower heads. Structurally, however, Isostylis flower heads are quite different from those of B. ser. Dryandra, having more in common with the erect flower spikes of other Banksia taxa. Specifically, Isostylis flower heads have an ovoid axis, suggestive of a greatly reduced flower spike, whereas Dryandra flower heads emerge from a flat receptable. Furthermore, Isostylis has thick follicles with a woolly coating, whereas Dryandra follicles are thin and hairless; and the involucral, common and floral bracts of Isostylis are unlike those of Dryandra.
The Isostylis species are all upright shrubs or trees, with a single trunk. They generally have serrate leaves, although in rare cases B. ilicifolia may have entire leaves.
B. subg. Isostylis was first published by Robert Brown in his 1810 Prodromus Florae Novae Hollandiae et Insulae Van Diemen; thus its full name, with author citation, is Banksia subg. Isostylis R.Br.Brown's arrangement was the first infrageneric arrangement of Banksia, making B. subg.Isostylis Banksia's first infrageneric taxon. Brown erected B. subg. Isostylis to contain B. ilicifolia, which was then the only known Banksia with a dome-shaped inflorescence. He did not explicitly name a type species for the subgenus, but B. ilicifolia is treated as the type because it was the only member when the subgenus was published.
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