Tilia americana
Malvaceae subfam. tilioideae
American basswood, American linden
blades (on flowering shoots) 5–15(–20) × 5–12+ cm, abaxial surfaces initially glabrate but for tufts of simple, forked, or fascicled hairs at some vein axils, or initially densely to sparsely stellate-hairy, then sometimes glabrescent, with or without tufts of simple, forked, or fascicled hairs at some vein axils, adaxial surfaces usually glabrous or glabrate.
blades usually unlobed, margins serrate, usually with domatia.
bracts 7–15 cm, notably reticulate-veined, notably hairy, glabrescent, or glabrate;
peduncle diverging from near or beyond midlength of bract.
axillary, usually dichasia, 3–24[–80]-flowered, rarely solitary flowers, associated with winged bract in Tilia.
weakly clavate, 4–15+ mm, notably hairy, glabrescent, or glabrate.
sepals 4–6(–9+) mm;
petals 5–9(–11) mm;
staminodes 4–7(–10) mm.
bisexual;
epicalyx absent;
sepals caducous, 5[–7], distinct, not petaloid, nectaries basal, adaxial;
petals 5, distinct, base not clawed;
androgynophore absent;
stamens [15–]40–60, ± distinct or in fascicles of 4–5;
anthers 2-thecate;
staminodes basally fused with stamens and petals absent;
gynoecium syncarpous.
ellipsoid to globose, 5–10 mm diam. 2n = 82.
capsules or nuts, indehiscent.
1–3, glabrous or hairy.
Tilia americana
Malvaceae subfam. tilioideae
In preparing this treatment, I tried to see merit in taxonomies in which more than one Tilia species native to the flora area are recognized. In the end, my experiences with specimens and my attempts at using taxonomies that purport to delineate distinct species and/or infraspecific taxa of Tilia in the flora area led me to agree with W. C. Ashby (1964), J. W. Hardin (1990), L. G. Hickok and J. C. Anway (1972), and H. Kurz and R. K. Godfrey (1962) that taxonomic recognition of more than one native Tilia species in the flora area is not tenable. I also concluded that recognition of infraspecific taxa within that one species in the flora area is not tenable.
If Tilia americana is partitioned (for example, by J. W. Hardin 1990), infraspecific taxa in the flora area may be characterized like so:
Variety americana has abaxial surfaces of leaves of flowering shoots initially glabrate but for tufts of simple, forked, and/or fascicled hairs at some vein axils.
Variety caroliniana has abaxial surfaces of leaves of flowering shoots initially sparsely to moderately stellate-hairy and with simple, forked, and/or fascicled hairs scattered and/or in tufts at some vein axils; attachments of the stellate hairs are usually fragile and the stellate hairs become sparser as seasons progress.
Variety heterophylla has abaxial surfaces of leaves of flowering shoots initially moderately to densely stellate-hairy and with simple, forked, and/or fascicled hairs scattered and/or in tufts at some vein axils; attachments of the stellate hairs are usually firm and the stellate hairs usually persist as seasons progress.
J. W. Hardin (1990) included Tilia mexicana Schlechtendal, native to Mexico (at least 14 states), in the circumscription of T. americana adopted here and treated it as T. americana var. mexicana (Schlechtendal) Hardin.
D. Pigott (2012) treated native tilias of North America as: Tilia americana var. americana, T. americana var. neglecta, T. caroliniana subsp. caroliniana, T. caroliniana subsp. floridana (extending into Mexico), T. caroliniana subsp. heterophylla, T. caroliniana subsp. occidentalis (Mexico), and T. ×stellata.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Tilioideae represent a narrow and fairly atypical circumscription of the former family Tiliaceae. The subfamily is unusual in the Malvaceae in being restricted to the Northern Hemisphere.
Genera 2 or 3, species ca. 40 (1 species in the flora).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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