Morphology and Development of Pistillate Inflorescences in Extant and Fossil Cercidiphyllaceae

Abstract

Comparison of the shoots, pistillate inflorescences, and infructescences of Joffrea speirsii Crane & Stockey from the upper Paleocene of Canada, Nyssidium arcticum (Heer) Iljinskaya from the upper Paleocene of southern England, and Trochodendrocarpus arcticus (Heer) Kryshtofovich from the lower Paleocene of Amur, eastern U.S.S.R., reveals considerable diversity in phyllotaxy, shoot growth, inflorescence position, and the number and crowding of follicles in each infructescence. Despite this diversity, the pistillate inflorescences of all these fossil Cercidiphyllum-like plants are directly comparable in basic organization, to inflorescences of extant Cercidiphyllum. These similarities add to the evidence that the fossil and extant taxa are closely and support the view that the condensed inflorescence of Cercidiphyllum evolved by reduction from an elongated form. In extant Cercidiphyllum each flower consists of a single carpel, but in fossil taxa flowers may contain either one or two carpels. The arrangement of carpels in bicarpellate flowers resembles that in extant Hamamelidaceae. The Cercidiphyllaceae contain a single genus, Cercidiphyllum, with two very similar species of dioecious trees, C. japonicum Siebold & Zuccarini native to Japan and central and western China, and C. magnificum (Nakai) Nakai native to Honshu (Spongberg, 1979). The Cercidiphyllaceae have been placed in the Hamamelidales (Cronquist, 1981) or treated as a separate order, Cercidiphyllales, within the Hamamelidae (Takhtajan, 1969). Cercidiphyllum thought to be related on the one hand to the Hamamelidaceae (especially Disanthus) and on the other to the Trochodendrales and Magnoliales (Cronquist, 1981: 167), although most authors agree that Cercidiphyllum an isolated genus separated by large morphological gaps from its closest living relatives. The pistillate reproductive structures of Cercidiphyllum are unusual: they superficially resemble an apocarpous flower with two to eight carpels, but the carpel orientation apparently anomalous, with the ventral suture directed abaxially. Swamy and Bailey (1949) supported the earlier hypotheses of Brown (1939), Harms (1916), and Solereder (1899), and interpreted the pistillate reproductive structure as a reduced inflorescence. As part of the evidence for this hypothesis Brown (1939) and Swamy and Bailey (1949) cited the elongated inflorescences of fossil Cercidiphyllum-like plants, which were widespread at middle and high latitudes of the Northern Hemisphere during the Upper Cretaceous and lower Tertiary (Brown, 1939, 1962; Chandrasekharam, 1974; Schloemer-Jiger, 1958). Although this hypothesis has been discussed by subsequent authors, the precise similarities between the fossil and extant inflorescences have remained obscure due to inadequate understanding of the fossil material. In recent years knowledge of these fossil plants has increased considerably (Crane, 1984; Crane & Stockey, 1985; Krassilov, 1976; Stockey & Crane, 1983). They are now known from seedlings, leaves, shoots, pistillate inflorescences, infructescences, seeds, and possible staminate inflorescences, and it clear that these extinct Cercidiphyllum-like plants are more closely to Cercidiphyllum than to any other genus (Crane & Stockey, 1985). In this paper we compare the I This work was supported in part by a United States National Science Foundation grant BSR-8314592 to PRC, and a NSERCC (National Sciences and Engineering Research Council of Canada) grant A6908 to RAS. We thank Dr. V. A. Krassilov, Institute of Biology and Pedology, Far-eastern Scientific Centre, Vladivostok, U.S.S.R., for the use of Figures 16-18 and for helpful discussions of the Amur material. We are also grateful to Paul and Chris Rechten for directing our attention to the material from Decker, Montana; to Mrs. Betty Speirs for collecting most of the specimens of Joffrea used in this study; and to P. K. Endress, E. M. Friis, and J. A. Wolfe for very helpful comments on an earlier draft of this manuscript. 2 Department of Geology, Field Museum of Natural History, Roosevelt Road at Lake Shore Drive, Chicago, Illinois 60605. 3Department of Botany, University of Alberta, Edmonton, Alta, Canada T6G 2E9. ANN. MISSOURI BOT. GARD. 73: 382-393. 1986. This content downloaded from 157.55.39.162 on Thu, 11 Aug 2016 05:16:57 UTC All use subject to http://about.jstor.org/terms 19861 CRANE & STOCKEY-CERCIDHYLLA(IAE 383 FluREs 1,2. ICEcdicpyUWMjaponWm Sieb. & Zucc.1. Two short shoots with young pi inorceas at leaves not the long styles and stigmas, and three hknles (BS) surruding at leaf on fie right in rescar on left shows a bract (B) s ing one of the four carpels, x 3.5.-2. Two curved short shoots showing leaf scars, axiflary bud (AB), with four folices, and bract (B) at ls of follicles, x 3.3. Sale bars, 2 mmshoots and sillate reproductive stuctures of extant Ceridphyllum with early Tertiary Cercidphyllum-llke plants from western Cnada (Joffrea peirii Cran & Stockey, 1985), southern England [Nymrim arcmicw (Heer) funskaya; Crane, 19841, and eastern U.S.S.R. [TmachodendrocarPus wctis (Heer) Kryshtofovich; Krassilov, 1973, 1976]. The nomenclature for fossil taxa follows that ted in Crane (1984), Crane and Stockey (1985), and Krassilov (1976). Discuson of the complexno and stematics of fossil Cecijhyflum-like inf iuctescencs outside the scope of this paw. Comparisons among fossil tama demonstrt considerable diversity in phyllotaxy, shoot growth, iorescen and the numnb and crowding of follin each infniuescence. However, thtre are fudmtal imilrities in construction of the pistiflate eproducWtive structures in the extant and fossil plants& These similarities add to the evidence that the fossil and extant taxa are closely related, explan some of the unusual morp ical fates of ext Cerci~dphylfl and facilitate more meaningl comparison of the gnus with other extant taxa in the Hamamelidae. ExTANr CERC1IDrPHYLLUm Extant Cercidphyllum has branches dirtiated into long and short shoots. In trees that we have examind, long shoot leaves are opposite, subopposite, or occasionally in irregular whorls of thre. Short shoots develop from the axillary buds of long shoot leaves. Each axillary bud has three bud-scales (FIs 1, 19); the outer and inner are positioned opposite to the second bud-scale and the leaf of the pdWing season. The new leaf develops opposite the inner budscale (Swamy & Bailey, 1949), and each short shoot bears a si leaf in each grow season (Fig. 1). Short shoot growth sympodial, contonumineah season thgh the ativy of a new axlay bud. The rsling short shoots are distiMily curved toward the long shoot on which they are born (iFg. 2). In fertile short shoots the pislate ino uene is terminal and consists of a short axi that has a coter of two to eight carpels at the apex This content downloaded from 157.55.39.162 on Thu, 11 Aug 2016 05:16:57 UTC All use subject to http://about.jstor.org/terms 384 ANNALS OF THE MISSOURI BOTANICAL GARDEN [VoL. 73 Ilk,~ ~ ~ ~~ %h IncV