Mesodescolea S.Archang.

Plant Fossil Names Registry Number: PFN001940

Act LSID: urn:lsid:plantfossilnames.org:act:1940

Author: S. Archangelsky

Rank: genus

Reference: Archangelsky, S. (1963): A new Mesozoic flora from Ticó, Santa Cruz Province, Argentina. – Bulletin of the British Museum (Natural History). Geology. 8(2): 47–92, 12 pls.

Page of description: 59

Type

Original diagnosis/description

Leaf bipinnate, oblong, typically 6 cm. ling × 4 cm. wide. Leaf rachis less than 1 mm. wide with deep longitudinal midfurrow. Pinnae opposite, decurrent, arising at 30° to rachis, lanceolate, with rather narrow base up to 4–5 cm. long × 1,5 cm. wide near middle and ending with single acute pinnule. Pinna rachis with pronounced midfurrow. Pinnules subopposite to alternate, arising at 30° to pinna rachis; pinnules with broad base and acute apex, up to 15 mm. long × 3 mm. wide, margins entire; lower margin markedly decurrent and connecting with upper margin of pinnule below. An unbranched midrib enters pinnules and extends to near apex.
Upper cuticle without stomata. Cells polygonal, square or rectagular, up to 40 μ long × 30 μ wide. Anticlinal walls usually pitted, up to 3 μ thick. Cell. surface usually with ridges having no definite orientation. Cuticle of lower surface having stomata except on veins. Cells on veins elongated, with conspicuous longitudinal ridges. Cells on lamina of irregular shape, usually with rounded contours; anticlinal wall about 2 μ thick, pitted. Cell surface with irregular ridges. Specialised small cells (trichome bases) present, surrounded by conspicuous series of radiating ridges which cross up to several rows of surrounding cells. Ridges at right angles or parallel to long axis of stomata, also conspicuous.
Stomata on lower cuticle typically monocyclic, oval or nearly round, with no definite orientation, typically 23–35 μ long, 45–60 per sq. mm. guard cells little or not at all sunken. Subsidiary cells not specialised, from 5–8, usually bearing ridges which can be normal or parallel to long axis of stoma. Guard cells with a conspicuous and constant rim surrounding mouth, sometimes interrupted at poles. Contact of guard cells and subsidiary cells generally covered by strong ridge reproducing roughly the outlines of guard cells.

Etymology

The genus Mesodescolea is dedicated to Dr. Horacio Descole, Tucumán, Argentina.