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Florissantia is an extinct malvaceous genus found in Eocene and Oligocene deposits in western North America, from Colorado to British Colunbia, and also in Miocene deposits in the Soviet Far East, to which is given the vernacular name of stone rose. Flowers, fruits and pollen are all found. Fossils of Florissantia were formerly placed in Porana (Convolvulaceae) and Holmskioldia (Verbenaceae). Florissantia is related to the living genera Fremontodendron and Chiranthodendron, being placed with them in the tribe Fremontodendreae.
Four species are recognised; Florissantia speirii (Lesquereux) Manchester, Florissantia quilchenensis (Mathewes & Brooke) Manchester, Florissantia ashwillii Manchester and Florissantia sikhote-alinensis (Krysh.) Manchester, on the basis of differences in perianth and anther morphology.
The genus was introduced in 1916 by Knowlton [a]. However his species is now considered a junior synonym of a plant then placed in Porana or Holmskioldia, and the current conception and extent of the genus is due to Manchester's 1992 paper 
The flowers of Florissantia are pedicellate, with a shallowly campanulate, 5-lobed, persistent, fused, calyx, and a missing or reduced corolla, and a short androgynophore. The androecium is composed of 5 bifurcate filaments, fused at the base, bearing a total of 10 anthers. The ovary is superior and 5-locular, and is surmounted with a single style.The pollen is oblate, 20-32 µm equatorial diam, 3(-4)-colporate, with short colpi and reticulate ornamentation. The fruit is elliptical, apparently indehiscent, and usually associated with a persistent calyx.
Florissantia ashwillii Manchester
Florissantia ashwillii is found in the lower Oligocene Goshen flora of Oregon, and at other probable middle or late Eocene (Sheep Rock Creek) and lower Oligocene (Summer Spring) localities in that state. The specific epithet honours Melvin S. Ashwill, who collected may of the best specimens of the species.
The original specimens were mistakenly associated with leaf fossils assigned to Viburnum palmatum Chaney and Sanborn.
The flowers of Florissantia ashwillii are borne on 0.6mm thick pedicels, at least 13mm long. The calyx is shallowly campanulate, and 21-31mm in diameter. It is composed of 5 membraneous sepals, which are fused for about half their length. The sepals have a prominent radiating reticulate venation, and are narrowed at their bases to conform to the outline of the androgynophore. Numerous, simple hairs, are found at the base of the sepals; these may represent nectaries. There are no petals. There is a short androgynophore up to 1.5mm in length which is thickened at its apex into a disk 1.5-1.7mm in diameter. The androecium is composed of 5 stamens which are fused at their base to form a circular sleeve around the base of the ovary. The filaments are 3.5-6.4mm long. The anthers (or half-anthers) are 1.0mm wide and 1.9mm long, elongate and tranversely septate. The ovary is superior, obovate, and composed of 5 cells, with a rounded to 5-angled cross-section and a single style.
The pollen is oblate, small (less that 30µm in equatorial diameter), isopolar, radially symmetric and tricolporate with short colpi. The equatorial cross-section is circular to rounded-triangular; in the latter case the colpi alternate with the angles. The surface of the pollen is reticulate with smooth muri and more or less angular luminae 0.4-1.0µm across.
The fruit consists of the enlarged ovary, associated with the persistent calyx and pedicel. It is elliptical, and circular to pentagonal in cross-section with a diameter of 4.1-5.6mm.
Florissantia quilchenensis (Mathewes & Brooke) Manchester
Florissantia quilchenensis is found in the Eocene of British Columbia (Quilchena, Chuckanut), Washington (Republic flora) and Wyoming (Green River Fm.). The specific epithet refers to the first locality.
The flowers of Florissantia quilchenensis are borne on 0.5-0.7mm pedicels, which are 16-21mm long. The calyx is shallowly campanulate, and 19-33mm in diameter. It is composed of 5 membraneous sepals which are fused for much (sometimes all) of their length, giving an outline which varies from distinctly 5-lobed to pentagonal or nearly orbicular. The sepals have a prominent radiating reticulate venation, and are narrowed at their bases to conform to the outline of the androgynophore. Numerous, simple hairs, are found at the base of the sepals; these may represent nectaries. Unlike in the other species, a corolla is present,. consisting of 5 small (3mm wide, 3.5mm long) obovate petals. The petals are thick-textured, with prominent subparallel reticulate venation, and are placed alternately to the sepals. The androgynophore is 2-3mm long and thickened into a disc at its apex. The androecium is composed of 10 stamens on filaments 4-5mm long. (The quality of preservation of specimens is inadequate to ascertain whether there are 10 simple filaments, or 5 bifurcate filaments.) The anthers are large, 2-3mm long, and curved. The ovary is obovate with rounded to 5-angled cross section, a single style, and a five-lobed stigma.
The fruit is composed of the enlarged ovary, and is 3.5-5.0mm in diameter and 5.0-6.0mm in height. It has five longitudinal ridges that meet at the apex, and a circular to pentagonal crosssection. The calyx and pedicel, and sometimes the corolla remains associated with the fruit.
Preservation of the specimens of this species is inferior to that of the best specimens of the other species, and neither nectaries nor pollen have been observed.
Florissantia quilchenensis has also been recorded under the names Holmskioldia quilchenensis Mathewes & Brooke and Hydrangea benderei auct. non Knowlton
Florissantia speirii (Lesquereux) Manchester
Florissantia speirii is found in the latest Eocene of Colorado (Florrisant flora), the late Eocene or early Oligocene of Montana (Ruby Basin), from several Eocene and Oligocene localities in Oregon, and from Wyoming.
The flowers of Florissantia speirii are borne a pedicel which is 0.6-1.0mm thick, and up to 38mm long. The calyx ix shallowly campanulate,.and 23-54mm in diameter. It is composed of 5 membraneous sepals, each with 5-7 prominent veins, fused for much (2/3rds-4/5ths) of their length, giving an outline which varies from distinctly 5-lobed to pentagonal or nearly orbicular. The lobes are rounded to pointed, with prominent radiating reticulate venation. There are no petals. The androgynophore forms a thick circular to rounded-pentagonal disc of diameter 2.4-4.0mm. The androecium is composed of ten anthers borne on 5 bifurcate filaments. The filaments are fused at their base to form a tube which surrounds the lower portion of the ovary. The filaments are 6-7mm long, with large (2-3mm long), globose anthers. The ovary is obovate, with a rounded to 5-angled crosssection, with a single style and 5 small stigmas.
The pollen is oblate, isopolar and radially symmetric, with an equatorial diameter in the region of 30µm. It is tri- or tetra-colporate, with short colpi. The equatorial crosssection is circular to rounded-triangular or rounded-quandrangular. The ornamention is reticulate with smooth muri and more or less angular lumina 0.4-1.0µm across, decreasing in size from the poles.
Preservation is sufficient to identify the internal architecture of the pollen wall. The exine is 770nm thick in total, with a foot layer 230-280nm thick, and the sexine tectate perforate with a roughly 300nm thick tectum.
The fruit is composed of the enlarged ovary, and is 8-11mm in diameter and 9-12mm in height. It has five longitudinal ridges that meet at the apex, and a pentagonal crosssection. The calyx and pedicel remain associated with the fruit.
Although hairs have not been observed at the base of the calyx, this region is sometimes darker coloured in specimens, which may correspond to the presence of pubescence.
Florissantia speirii has also been recorded under the names Florissantia physalis Knowlton, Holmskioldia speirii (Lesquereux) MacGinitie, Porana similis Knowlton and Porana speirii Lesquereux
Florissantia sikhote-alinensis (Krysh.) Manchester
Florissantia sikhote-alinensis is found in the Miocene of Sikhote-Alin in the Soviet Far East. It has also been recorded under the name Porana sikhote-alinensis Krysh..
I have encountered a mention of Florissantia similkameenensis, from the Eocene Tranquille Shale of British Columbia. From the little I have seen (a low resolution photograph) this is not obviously distinct from Florissantia quilchenensis (though no petals were identifiable on the photograph).
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