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Taxus leaves are differentiated from those in related taxad genera by papillose cells that define the stomatic apparatus (Dilcher 1969; Florin 1931, 1948c, 1951, 1958). The Wallichiana Group is regarded ancestral to the other groups by leaves having angular epidermal cells as seen in transverse (T) section, and by having a uniform papillose abaxial surface bordered by a narrow margin of smooth cells, most often 4 cells wide.

This apparatus includes 48 small subsidiary papillose cells, which encircle each stoma (Florin ring, Florin 1931), and adjacent (accessory) papillose cells that often intergrade into a marginal region of smooth cells. The Baccata Group, which may have been derived from the Wallichiana Group by gradual loss of stomata and papillae, differs by smaller elliptically shaped epidermal cells (as seen in T-section), and by less developed papillae on the abaxial leaf midrib.

These were returned with sketches, notations, leaf fragments and Spjut's annotation labels via the US National Arboretum (NA).

Leaves from fresh specimens, on the other hand, although easy to section, lack color distinction except when kept in a refrigerator, then, usually within a few days, subsidiary cells (cells surrounding the stomata), or only the guard cells, may turn orange.

This change in color makes it easy to count stomata rows.

The secondary compounds, however, have yet to be identified, but apparently are phenolics that oxidize slowly after a specimen is collected, except for species in the Sumatrana Group in which a change in color occurs more rapidly upon dryingwithin a week after collection.

Resinous like substances are generally observed in cell walls of the leaf epidermis and mesophyll layers. 1999, Seasonal variation of neutral and basic taxoid contents in shoots of European Yew (Taxus baccata).

Index Kewensis was consulted for the original publication and other taxonomic papers concerning species names and their authors.

The original publication and other literature as cited were reviewed.

Twenty-four species and 55 varieties of Taxus are identified in taxonomic keys and in detailed descriptions by morphological characters.

The species concept is based on pattern recognition from study of more than 1,000 dried herbarium specimens and another ~ 300 fresh specimens from plants collected throughout the range of the genus (shipped via express next day delivery), including many cultivars at the Secrest Arboretum in Ohio, The Royal Botanic Gardens at Kew, and The Botanical Garden in Paris; data for 845 specimens are summarized in Spjut (2007a). brevifolia was discovered in 2011 while conducting field work for Veratrum californicum in the Klamath Region of the Pacific Northwest (Spjut 2014, abstract submitted). isodichotomous), color of leaf epidermal cells and stoma bands, persistence of scales at base of branchlets, bud-scale texture and size, change in color of branchlets from 1st to 2nd yr, leaf arrangement, leaf shape, leaf thickness, leaf curvature lengthwise and across both surfaces, changes in leaf curvature near margins and along midrib, shape of cones in bud and at maturity, whether seed develops on current season growth or older branchlets, shape and color of seed, shape of epidermal cells as seen in cross-section, color of leaf epidermal and mesophyll layers in leaf sections, number of marginal cells without papillae, number of stomata rows in a stomata band, shape of parenchyma cells in the leaf spongy mesophyll, and others (character list in DELTA format, research proposal on Taxus, USDA Memorandum, Spjut 1995).

Occasionally, leaf sections were photographed using color slide film from which prints were then obtained (especially in the Wallichiana Group).

The slides, photographs and packets were retained with the voucher specimens as also shown for species of the Wallichiana Group.

Stafleu and Cowan (TL-2, Taxonomic Literature, 1976-1988) were consulted for information on the location of authors’ type specimens; however, most species of Taxus lacked designated types; thus, it was necessary to designate types.

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