Eocene “Chusquea” fossil from Patagonia is a conifer, not a bamboo

Chusquea oxyphylla Freng. & Parodi, 1941, a fossilized leafy branch from the early Eocene (52 Ma), late-Gondwanan Laguna del Hunco biota of southern Argentina, is still cited as the oldest potential bamboo fossil and as evidence for a Gondwanan origin of bamboos. On recent examination, the holotype specimen was found to lack any typical bamboo characters such as nodes, sheaths, ligules, pseudopetioles, or parallel leaf venation. Instead, it has decurrent, clasping, univeined, heterofacially twisted leaves with thickened, central-longitudinal bands of presumed transfusion tissue. These and other features allow confident placement in the living Neotropical and West Pacific disjunct genus Retrophyllum (Podocarpaceae), which was recently described from the same fossil site based on abundant, well-preserved material. However, the 1941 fossil holds nomenclatural priority, requiring the new combination Retrophyllum oxyphyllum (Freng. & Parodi) Wilf, comb. nov. No reliable bamboo fossils remain from Gondwana, and the oldest South American bamboo fossils are Pliocene. Chusquea joins a growing list of living New World genera that are no longer included in Paleogene Patagonian floras, whose extant relatives are primarily concentrated in Australasia and Malesia via the ancient Gondwanan route through Antarctica.

Lower Cretaceous conifers from Apple Bay, Vancouver Island: Picea-like leaves, Midoriphyllum piceoides gen. et sp. nov. (Pinaceae)This paper is one of a selction of papers published on the Special Issue on Systematics Research.

A diverse assemblage of fossil conifer leaves was identified in calcareous marine concretions from the Lower Cretaceous (Valanginian–Hauterivian) Apple Bay locality, Vancouver Island. Of the hundreds of isolated leaf fragments, most show affinities to Pinaceae. Leaves with closest similarities to Picea (spruce) were studied using cellulose acetate peels. Picea-like leaves vary in cross-section from rhomboidal, pentagonal, triangular, to ovoid. One fused vascular bundle with a centrally located ray and abaxial sclerenchyma is surrounded by a circular endodermis and transfusion tissue. Mesophyll is plicate containing two lateral external resin canals surrounded by a sclerenchyma sheath. Hypodermal fibres are one to three layers thick, except in areas of stomata. Leaves are amphistomatic, with sunken guard cells. Vascular bundles are identical anatomically to Picea; however, plicate mesophyll is similar to that in leaves of Pinus. Extensive sclerenchyma in the hypodermis and surrounding resin canals differs from that in most extant Picea. The major difference between these leaves and those of Picea is leaf shape. These fossil leaves probably belong to an extinct pinaceous conifer, and are described as Midoriphyllum piceoides gen. et sp. nov. Similar evidence from Cretaceous seed cones suggests that like the angiosperms, the Pinaceae were undergoing rapid mosaic evolution during the Lower Cretaceous.

Pinus haboroensis sp. nov. and the affinities of permineralized leaves from the Upper Cretaceous of Japan

A new species of Pinus is described based on permineralized needles from the Sankebetsugawa, Haboro, and the Koyanosawa, Ikushumbetsu, Mikasa City, Hokkaido, Japan. Leaf fragments were discovered in calcium carbonate nodules with abundant ammonites dated as Santonian–Senonian (Upper Cretaceous). The leaves, borne in fascicles of three or four, are 0.9–1.1 mm in radial and 1.5–1.8 mm in tangential diameters, and fragments up to 0.5 cm long have been recovered. The vascular strand is double and bundles are separated by a large anchor-shaped band of sclerenchyma fibers. Transfusion tissue up to four cells wide and a long-base triangular endodermis with an irregular outline surround the vascular tissues. Six to eight medial and external resin canals occur within the band of small plicate mesophyll cells three or four cells wide. The uniform hypodermis from one to four cells thick lies beneath thick-walled elliptical epidermal cells. These amphistomatic leaves with deeply sunken stomata most closely resemble those of Pinus coulteri D. Don, subgenus Pinus, section Pinus, subsection Sabinianae and have added significantly to our knowledge of permineralized Cretaceous pine needles. Pinus haboroensis sp. nov. is closely compared anatomically with the other Upper Cretaceous pines from Japan and North America and primitive needle characters are discussed. Emended diagnoses for P. flabellifolia Ogura and P. bifoliata Ueda and Nishida are presented, including a description of their possible affinities to sections and subsections of the genus Pinus.

Light and electron microscopy of embryo development in perennial and annual Medicago species

The embryo of perennial Medicago sativa L. and annual M. scutellata (L.) Mill. have similar growth stages, but the perennial embryo is smaller and its rate of growth is slower than that of the annual by about 3 days. Transfer cells in the suspensor and embryo sac of late heart stages suggest different major pathways of nutrient flow in the two species. Transfusion tissue at the base of the embryo sac in the ovule of M. scutellata may facilitate solute transport and promote rapid embryo growth. Plastids in the suspensor cells of heart and late heart stages of the two species contain a dense matrix, membrane-bounded plastid vacuoles, starch, and a dense core. The plastid core in M. sativa has stacked tiers of straight tubules about 24 nm in diameter, suggesting that these specialized plastids are like tubular chromoplasts. Plastid vacuoles arise from the periphery of dense cores and apparently discharge electron-translucent contents into the suspensor cytoplasm. Plastid vacuoles may play a role in suspensor metabolism and thus influence embryo development.

The anatomy of the leaf of red pine, Pinus resinosa. II. Vascular tissues

The anatomy and ultrastructure of the endodermis and enclosed vascular tissues of the midregion of the mature secondary needle-leaf of Pinus resinosa are described. Within the uniseriate endodermis are two vascular traces surrounded by transfusion tissue. The endodermal cells have differentially thickened walls which lack Casparian strips but are lignified. Plasmodesmata traversing pit regions form a symplastic interconnection between mesophyll, endodermal, and transfusion parenchyma cells. In the lateral bundle region plasmodesmata extend this symplastic pathway across the cell walls of subjacent transfusion parenchyma and richly protoplasmic albuminous cells to the metaphloem. Four distinct types of transfusion tracheids have been defined on the basis of cell shape and location. Transfusion tracheids in the lateral bundle regions form direct radial connections between metaxylem and endodermis.