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Tiliaceae

TILIA. Although our species are not absolutely limited, it seems necessary to restore T. pubescens to specific rank, and so to recognise three species [1], viz. —

T. AMERICANA, L., with ample leaves essentially glabrous, thickish and firm, green on both faces, the upper lucid; floral bract usually tapering into a stalked base (except the uppermost); fruit ovoid, usually lightly costate.

T. PUBESCENS, Ait., with smaller and mostly thinner leaves, distinctly pubescent beneath, yet often glabrate in age: floral bract usually rounded at base and sessile or hardly stalked: fruit globular. I do not adopt the older name of T. Caroliniana, Mill. Dict.; for the original character, as well as that of Marshall and Wangenheim, points to T. Americana rather than to T. pubescens. Probably to that species also belongs the T. pubescens of the Nouveau Duhamel. — The var. LEPTOPHYLLA, Vent., is well marked by its larger and thin leaves. It is hardly possible to combine this form with T. americana, and its habitat is much more southern.

T. HETEROPHYLLA, Vent., the T. alba of Michx., but not of Aiton, is well marked by its ample leaves of ovate outline (not rounded as in the true T. alba [2] of S. E. Europe), whitish or silvery beneath: floral bract tapering to a very short-stalked or sessile base, usually elongated, and the peduncles still longer; the fruit globular. It strictly belongs to the Alleghany region, from Southern Pennsylvania to Florida. The original reference of Aiton's T. alba to America was corrected in the second edition of the Hortus Kewensis. But having been copied by Ventenat, under his T. rotundifolia, the mistake has been kept up by Bayer in his Monograph, who places it under his T. heterophylla-nigra, and has two forms from Kentucky, both undoubtedly T. heterophylla.

T. MEXICANA, Schlecht., which Bayer makes a variety of T. pubescens, is probably a good species. The floral bracts taper to a slender-stalked base.

[1] Current opinion recognises only two species of Tilia in North America, the highly variable T. americana of the eastern United States, adjacent parts of Canada, and northeastern Mexico, and T. mexicana of the highlands of southern Mexico. Previously the four species given here were recognised, the second under the name T. caroliniana. Other writers have recognised many more species.
[2] This is correctly known as T. tomentosa.

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