Arnold, Chester A. University of Michigan, Ann Arbor, Michigan.
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A group of Mesozoic plants first recognized in 1925. The remains consist of palmately compound leaves with 3–6 lanceolate leaflets previously known as Sagenopteris phillipsi, pinnately branched microsporophylls (named Caytonanthus arberi) that bore winged pollen in four-chambered microsporangia, and fruit-bearing inflorescences, Caytonia (with two species), which bore a dozen or more globular, short-stalked fruits in subopposite rows. Each fruit was 0.2 in. (5 mm) or less in diameter. Near the attachment stalk at the lower part of the fruit was a small transverse lip beneath which was a minute depression marking the place where a small opening formed at pollination time. This opening admitted the pollen into the interior, where small orthotropous ovules were attached to the surface. The inflorescence thus resembled a simply pinnate frond, of which the individual pinnules were curved so as to enclose the seeds. When first discovered, it was believed that the flap served as a stigmatic surface to receive the pollen in a manner similar to the stigma of a modern flower. Later it was found that the pollen actually entered the young fruit through the small opening and germinated on the nucellus of the ovule after the manner in gymnosperms (Pinopsida). The Caytoniales appear related to the pteridosperms. They range from the Triassic to the Cretaceous. See also: Paleobotany
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