Onostrobus elongatus ROTHWELL et STOCKEY

Onostrobus elongatus ROTHWELL et STOCKEY sp. nov.

Text-figs 1–3

H o l o t y p e. (hic designatus) Paleobotanical specimen CASG 3,888 housed in the Geology Collections, California Academy of Sciences, 55 Music Concourse Drive, San Francisco, CA 94118, USA.

R e p o s i t o r y. Geology Collections, California

Academy of Sciences, San Francisco, California, USA.

P l a n t F o s s i l N a m e s R e g i s t r y N u m b e r.

PFN003376 for new species.

E t y m o l o g y. The specific epithet elongatus refers to the overall shape of the cone.

T y p e l o c a l i t y. Streambed located in the southwest corner of Section 12, T30N, R7W of the Ono Quadrangle, a short distance from the town of Ono California, USA.

S t r a t i g r a p h y a n d a g e. Upper Chickabally Member, Budden Canyon Formation, Early Cretaceous; Aptian Age; Bedoulian Stage.

S p e c i f i c d i a g n o s i s. Cone more than 16.1 cm long and 2.1 cm wide, with thin, foliate cone scales. Axis with parenchymatous pith and secondary xylem cylinder lacking resin canals; axis stele dissected by divergence of xylem to bract/scale complexes. Bract/scale complex vasculature of three traces forming inverted U-shape in scale base, opening out into single plane to become straight; dividing into several strands in scale base. Bract with at least one accompanying resin canal; bract trace of few loosely arranged tracheids. Large, apparently lysigenous canals in cone axis; two canals abaxial to vasculature of each bract/ scale complex. Scales with prominent abaxial and adaxial bands of hypodermal sclerenchyma; resin canals abaxial, adaxial and between vascular bundles in ovuliferous scale. Embryos with ca. 8–9 cotyledons.

(single arrowhead) basally and row of several xylem bundles (multiple arrowheads) more distally. Note pairs of large resin canals (r) associated with each diverging OS trace, some of which branch CASG 3,888 B top No. 27 x6. c: Cross section of OS trace with small holes in wood that resemble resin canals (arrows) among radial rows of incompletely preserved tracheids. CASG 3,888 B side No 71 x36. d: Tangential section showing inverted trilobed, U-shaped OS trace and scattered tracheids of bract trace (within circle) just peripheral to divergence from cone stele. CASG 3,888 B side No. 69 x13. e: Radial section of cone showing diverging xylem to bract/ scale complex. CASG 3,888 B side No. 42 x10. f: Tangential section of cone showing ovuliferous scale (sc) with two inverted seeds (s) separating from fleshy bract (b) immediately distal to divergence from cone axis. Bract has one resin canal and no vascular bundle at this level. Note bract and ovuliferous scale separate from margins, inward (arrows) CASG 3,888 B side No. 17 x17. g: Cross section at cone periphery showing ovuliferous scales distal to separation from axis. CASG 3,888 B top No. 24 x7. h: Anatomy of ovuliferous scale in cross section showing segmented bract xylem surrounded by parenchyma, with several layers of sclerenchyma cells toward periphery of both abaxial and adaxial surfaces. Note positions of small resin canals (arrowheads) with incompletely preserved cells of epithelial lining. See also parenchymatous cortex of axis (ac). CASG 3,888 B top No. 22 x31.

D e s c r i p t i o n. The holotype is an incomplete ovuliferous cone that is cylindrical and the preserved segment has an extended length/width ratio for a pinaceous seed cone (i.e., ca. 7.7:1; Text-fig. 1a). Despite missing both base and apex, and having been abraded and weathered after fossilization, the specimen measures 16.1 cm long and 2.1 cm in diameter. It preserves the bases of helically arranged bract/scale complexes at the surface ( Text-fig. 1a, b), but more apical regions of the scales are missing. Therefore, the presence or absence of a scale apophysis or umbo is unknown.

In cross sections the cone has a parenchymatous pith of cells 20–56 µm in diameter (mean = 37.9 µm, n = 50), with prominent walls. The pith is surrounded by a zone of dense wood made up of radial rows of tracheids up to 35 cells wide (Text-figs lb, 2a). Tracheids are shrunken away from each other, and range 20–30 µm in diameter. Ray cells are not preserved, but there are radially elongated spaces that separate some rows of tracheids that represent the positions where rays originally were located ( Text-fig. 2a). Such spaces are 10–20 µm wide suggesting that the rays were uniseriate and constructed of parenchyma cells of about the same diameter. The woody cylinder is interrupted by the divergence of vascular tissue to bract/scale complexes ( Text-fig. 1b). No resin canals are present in the pith or wood of the cone axis ( Text-figs 1b, 2a).

The cone axis has a conspicuous system of axial canals in the cortex ( Text-figs 1b, e, 2a, b), and two are associated with the divergence of each bract/scale complex ( Text-fig. 2a, b). Such canal pairs are consistently located abaxial to the diverging ovuliferous scale vascular bundle in the cortex of the cone axis ( Text-figs 1b, 2a). They are large and conspicuous near the stele (680–1,000 µm) but decrease in size rapidly toward the periphery of the axis ( Text-fig. 2a). A few canals in each cross section are in the process of branching ( Text-fig. 1b, at brc, Text-fig. 2a, at brc). Branching canals are dilated to nearly twice the diameter of other resin canals (i.e., up to 1.4 mm; Text-figs 1b, 2a). An epithelial lining appears to be absent from these canals ( Text-fig. 3g), and they often display some black contents ( Text-figs 1b, 2b).

Although no resin canals have been found in the stele of the cone axis, there are possible examples in the secondary xylem of diverging ovuliferous scale traces (e.g., Text-fig. 1c). Most sections show no evidence of such structures (e.g., Text-fig. 3a, c), but in a few sections there are round structures 31–42 µm in diameter that possibly could be resin canals. Such structures sometimes occur in a row that is close to the interior of the secondary xylem ( Text-fig. 3g), and typically have a gray, non-cellular rim, but a few show remnants of what may have been an epithelial lining ( Text-fig. 3g, at arrow).

Each bract/scale complex consists of an ovuliferous scale with two adaxially positioned and inverted seeds near the base. The ovuliferous scale is subtended by a short fleshy bract in which one lateral resin canal is preserved ( Text-fig. 1f), but there is no vascular tissue distal to divergence of the bract. Ovuliferous scales are parenchymatous at the level of seed attachment ( Text-fig. 1f), but have several layers of both abaxial and adaxial hypodermal sclerenchyma at more distal levels Text-figs 1b, 2a). As seen in radial sections, the ovuliferous scale xylem separates from the stele at about a 90° angle and then bends gently distally before entering the base of the scale ( Text-fig. 1e). In tangential views from the periphery of the stele to the periphery of the cone axis, the scale xylem first appears as bulges ( Text-fig. 3a), then separates as three closely adjacent bundles that form an inverted U-shape ( Text-fig. 3b). In successively more tangential sections, the scale xylem opens out into a linear, three-lobed configuration ( Text-fig. 3c). In transverse sections the scale xylem shows a similar three-lobed configuration within the axis cortex ( Text-fig. 3d), and then appears as a straight band of xylem at the margin of the axis ( Text-fig. 3e). Shortly after separating from the axis, at the level where seeds are attached, the scale xylem separates into several wide bundles ( Text-fig. 3f).

Immediately distal to divergence from the cone axis the ovuliferous scales have several layers of both abaxial and adaxial hypodermal sclerenchyma and interspersed parenchyma ( Text-fig. 1h) that gives those with incompletely preserved histology the appearance of having a dark peripheral zone ( Text-fig. 1b, g, 2a, b). The ground tissue consists of parenchyma cells between and surrounding the vascular bundles ( Text-fig. 1h). There are also a number of small resin canals with an incompletely preserved epithelial lining abaxial to, adaxial to, and between the vascular bundles ( Text-fig. 1h, at arrowheads). Tissue preservation deteriorates in quality at more distal levels of the free bracts ( Text-fig. 1b, g at lower left), where neither vascular tissue nor resin canals can be identified.

Before separating from the cone stele, vasculature of the bract/scale complex appears as lateral bulges of tracheids in longitudinal sections ( Text-fig. 3a). The ovuliferous scale xylem separates from the stele of the cone axis as three adjacent xylem strands that form an inverted U-shaped bundle ( Text-fig. 3b, Tab. 1). Toward the periphery of the cone axis cortex, the three bundles fuse to form a U-shaped bundle that opens out into a more linear three-lobed bundle ( Text-figs 2a, 3c, d), and then becomes an unlobed linear bundle in cross sections ( Text-figs 2a, 3e, f). Distal to the level where the ovuliferous scale separates from the cone axis the bundle divides into 8–10 strands ( Text-figs 2a, b at arrowheads, 3f). More distally in the free ovuliferous scales, incomplete preservation precludes identification of vascular tissue ( Text-figs 1b, 2a, b).

The bract separates from the ovuliferous scale immediately after the bract/scale complex becomes free from the cone axis. The bract trace divides from the cone integument (i), cellular megagametophyte (m), and hypocotyl (h) of embryo. CASG 3,888 E top No. 3 x20. d: Cross section of winged seed attached to adaxial surface of cone scale in (b) with other tissues removed to emphasize wing tissue . CASG 3,888 B top No. 32 x16. e: Cross section of seed showing integument (i), cellular megagametophyte (m), and embryo at level of cotyledons (at arrowheads) . CASG 3,888 E top No. 3 x23 .

axis stele separately from the ovuliferous scale vasculature. At the level of separation it consists of a small number of loosely arranged tracheids (within circle in Text-figs 1d, 3b). At more distal levels, the bract is constructed of closely spaced parenchyma cells and has one lateral resin canal, but shows no evidence of the bract trace ( Text-fig. 1f).

Two inverted winged seeds are adaxially attached near the base each ovuliferous scale ( Text-figs 1a, f, 2b, d). Seeds have a body that is ellipsoidal in shape ( Text-figs 1b, f, 2b, d), ca. 6 mm long and ca. 3 mm in diameter in the midregion. The integument has a prominent zone of cells that are incompletely preserved, but appear to have thick walls ( Text-figs 1b, f, 2b, d). To the inside of that zone there are one or two layers of larger thin-walled cells ( Text-fig. 2d, e). The outer integumentary zone surrounds the seed body. It consists of parenchyma cells ( Text-fig. 2b, d, e) that are continuous with and have a histology that is identical to that of a seed wing ( Text-fig. 2b, d, e) that extends both laterally and basally ( Text-fig. 2b, d).

Several seeds contain a cellular megagametophyte of closely spaced thin-walled cells ( Text-fig. 2c, e). A few seeds also contain a well-preserved cotyledonary embryo ( Text-fig. 2c, e). Embryos are straight. They consist of a hypocotyl that is round in cross sections, consisting of a central zone of presumed vascular tissue and a peripheral cortical zone ( Text-fig. 2c). Embryos have several cotyledons apically that are triangular in cross sections ( Text-fig. 2e). The exact number of cotyledons cannot be determined from the available evidence, but the seed in Text-fig. 2e has five (at arrowheads), that make up somewhat more than 180° of the circumference of the embryo, suggesting there are a total of ca. 8–9.