ISSN 1346-7565 Acta Phytotax. Geobot. 72 (1): 1–21 (2021) doi: 10.18942/apg.202009 A Multicarpellary Apocarpous Gynoecium from the Late Cretaceous (Coniacian–Santonian) of the Upper Yezo Group of Obira, Hokkaido, Japan: Obirafructus kokubunii gen. & sp. nov. 1,* 2 3 YUI KAJITA , MAYUMI HANARI SUZUKI AND HARUFUMI NIshIDA 1Iriomote station, Tropical Biosphere Research Center, University of the Ryukyus, 870, Uehara, Taketomi, Okinawa 907–1541, Japan. *[email protected] (author for correspondence); 2Tama, Tokyo 206–0003, Japan; 3Faculty of Science and Engineering, Chuo University, 1–13–27 Kasuga, Bunkyo, Tokyo 112–8551, Japan Obirafructus kokubunii gen. & sp. nov. (family Incertae Sedis; order Saxifragales) is proposed based on a permineralized reproductive axis bearing at least 42 spirally arranged follicles. No bracts, perianth, stamens, nor their vestiges are present on the axis or the follicle stalk. It is therefore part of single flower and not an inflorescence. The axis is 57 mm long, woody, and contains scalariform perforations on the vessel walls. The flower is inferred to be unisexual, as in Cercidiphyllaceae (Saxifragales). The lower part, which may have borne male organs, is missing. The follicles consist of a conduplicate carpel with marginal placentas alternately bearing 90–100 seeds in two rows. The follicle has dorsal and ventral ridges and the ventral suture dehisces at maturity. The carpel probably has an apical style and stigma at anthesis. The ovules are bitegmic, anatropous. A nucellar cap plugs the micropyle. The seeds are slightly winged, which may represent hydrochory and/or anemochory. Based on these features, Obirafructus kokubunii probably inhabited a fluvial plain. The follicle clusters of Joffrea and Jenkinsella (fossil Cercidiphyllaceae) apparently resemble those of O. kokubunii; but they represent inflorescences. Obirafructus kokubunii adds a new morphotype to the past diversity of basal Saxifragales. Key words: anatomy, Cercidiphyllaceae, eudicot, follicle, fossil, inflorescence,Jenkinsella , Joffrea, mor- phology, Saxifragales The fossil described here was found in a cal- ing many follicles and is reminiscent of the mor- careous concretion that was collected along the phologies of some extant and comparable fossil Obirashibe River in Obira, Hokkaido, Japan, families of Saxifragales, sensu Angiosperm Phy- where Late Cretaceous shallow to offshore ma- logeny Group IV system (2016). Among the Saxi- rine sediments of the Haborogawa Formation of fragales, the fossil shows morphological similar- the Yezo Group occur. Nishida (2006) first tenta- ity to Cercidiphyllaceae, both living and fossil tively reported the specimen to be a ‘Cercidiphyl- forms (Swamy & Bailey 1949, Spongberg 1979, lum-like hamamelid’. The fossil-bearing strata Crane 1984, Crane & Stockey 1985, Feng et al. was exposed along the main stream of the Obi- 2000, Golovneva & Alekseev 2017). The Cercidi- rashibe River. The age has been estimated to cor- phyllaceae include only two extant species that respond to the Coniacian to Santonian period are restricted to Japan, China, and Korea. Their based on the associated marine fauna (Takashima fossil records extend back to the early-middle et al. 2004). An ammonite, Gaudryceras sp. (Fig. Aptian (Golovneva & Alekseev 2017). In this 1A), in the same concretion often occurs in the study, we describe the specimen as a new fossil Haborogawa Formation and does not contradict genus of Saxifragales, and particularly similar to the age estimation. Cercidiphyllaceae, without designating a particu- The Cercidiphyllum-like hamamelid fossil is lar family due to scarce information regarding a permineralized reproductive woody axis bear- Cretaceous plants. 2 Acta Phytotax. Geobot. Vol. 72 The fossil exhibits detailed anatomical infor- nearly mature before dehiscence. The fixed mate- mation reminiscent of the morphological and rials were dehydrated in an ethyl and tertiary-bu- functional diversity of basal Saxifragales, or tyl alcohol series and embedded in paraffin. Sec- more widely, of early Eudicots during their early tions 10 µm thick were cut with a RM2125RTF diversification in the Cretaceous. We compared rotary microtome (Leica Microsystems, Wetzlar, the seeds, follicles, and follicle clusters of the fos- Germany) and stained with Hematoxylin (Sig- sil with specimens of Cercidiphyllaceae to show ma), Safranin-O (Merck), and Fastgreen (Sigma). morphological diversity of the seemingly similar Sections of both the fossil and extant C. japoni- dispersal organs. For comparison, the follicle cum were mounted in Canada balsam and exam- anatomy of living Cercidiphyllaceae (i.e., Cerci- ined under a BX–50 light microscope (Olympus diphyllum japonicum Sieb. & Zucc. ex Hoffm. & Optical Co. Ltd., Tokyo, Japan). Images were Schult.) was also evaluated in this study. captured with a D–20 digital camera system (Pix- era Corporation, California, USA). The numerical geological ages used in this pa- Material and Methods per adhere to the International Chronostrati- graphic Chart (Cohen et al. 2013: revised version The fossil material was embedded in a calcar- May 2019). eous sandy siltstone concretion Kokubun NSM PP-9374 (original sample number: Kokubun HKP0001), which was collected in the middle Results reaches of the Obirashibe River, Obira town, Hokkaido, Japan. The concretion was cut into Systematic Description several pieces with a Mini-lab-cutter MC110 dia- mond slab saw (Maruto Instrument Co., Ltd., To- Phylum Magnoliophyta kyo, Japan) to obtain both transverse and longitu- Order Saxifragales dinal planes of the embedded reproductive shoot. Family incertae sedis For anatomical observations, the cutting planes were peeled sequentially using a cellulose-ace- Obirafructus Y. Kajita & H. Nishida gen. nov. tate peeling technique (Joy et al. 1956) to obtain Permineralized angiosperm reproductive shoot, consist- serial peels and to make microscope slides of the ing of a woody axis bearing a number of spirally arranged selected peels. Non-destructive images of the follicles. Axis in fruiting stage elongate, eustelic; vessels concretions were also obtained using a ScanX- with scalariform perforation plates. Follicle elongate fusi- form to falcate, tapering distally, dehiscing along ventral mate-A130S145 X-ray CT scanner (Comscantec- longitudinal suture; lateral surface transversely striate; no Co., Ltd., Yokohama, Japan) to confirm the placenta marginal. Dorsal midrib of follicle and each side anatomical reconstruction and to search for other of ventral suture ridged, 3-veined, 1 dorsal and 2 ventral. notable structures in the concretion. Whole piec- Follicle wall 3-layered, with pericarp, vascularized meso- es of the sectioned concretion and the microscop- carp, and fibrous sclerenchyma endocarp. Seeds numer- ous, flat, in 2 rows along ventral suture, one above the ic slides were deposited in the Tsukuba Research other. Seeds bitegmic, anatropous, winged; wing devel- Department of the National Museum of Nature oped on upper side of main seed body. Seed coats 2, inner and Science in Tsukuba, Ibaraki, Japan. and outer; inner seed coat thin; outer seed coat constitut- For anatomical comparisons, follicles of ex- ing wing and lower fibrous layer. Nucellar wall thickened tant Cercidiphyllum japonicum were collected below endostome, forming a nucellar cap. from the Koishikawa Botanical Garden of the Graduate School of Science of the University of Obirafructus kokubunii Y. Kajita & H. Nishida Tokyo, Japan, and fixed with FAA (formalde- sp. nov. — Figs. 1B–D, 2–10, 11D & 12C, D hyde: 70% ethyl alcohol: acetic acid = 1 : 18 : 1). Permineralized angiosperm reproductive shoot consist- The follicles were determined to be immature or ing of a woody axis bearing more than 42 conduplicate February 2021 KAJITA & AL. — Obirafructus kokubunii gen. & sp. nov. 3 FIG. 1. X-ray CT images of calcareous concretion containing a part of reproductive shoot of Obirafructus kokubunii gen. & sp. nov., specimen Kokubun NSM PP-9374. (A) Ammonite, Gaudryceras sp., embedded in same nodule. Diameter of ammonite shell is about 1 cm. (B) Cross section of main axis, two follicles, and two follicle bases (arrowheads). (C) Radial longitudinal section showing main axis bearing stiped follicles containing numerous seeds. (D) Tangential longitudinal section of a follicle showing two rows of seeds. Note wing tissue on upper side of each seed. f, follicle; fs, follicle stalk; mx, main axis; s, seed; w, seed wing. B–D, Scale bar = 1 mm. follicles in 5 : 8 phyllotaxy. Axis in fruiting stage, more constituting wing and lower fibrous layer, attached to pla- than 57 mm long, 2–5 mm in diam., eustelic; vessels with centa on winged side, vascularized by a single bundle on scalariform perforation plates. Follicles elongate fusiform upper middle portion of wing to chalazal end of nucellus. to falcate, 30–40 mm long, 3 mm in diam., short-stiped, Nucellar wall membranous, thickened below endostome abruptly tapering distally, dehiscing along longitudinal to form a nucellar cap. ventral suture; lateral surface transversely striate; cross Typus. Kokubun NSM PP-9374 (fruits in concretion section nearly round with semicircular dorsal ridge and block and microscope slides prepared from it) deposited ventral ridge splits at middle along longitudinal suture. in the Paleobotanical Collection of the National Museum 3-veined, 1 dorsal and 2 on each side of ventral suture. of Nature and Science in Tsukuba, Ibaraki, Japan. Follicle wall 3-layered; pericarp thin, consisting of an epidermis