Flowering Plants: Smartweeds to Hazelnuts

Betulaceae—Birch Family

180 I SMARTWEEDS TO HAZELNUTS The wood of overcup oak is hard, heavy, strong, and durable. It has been used in interior finishing, for cabinets, as fuel, and for fence posts. Hybrids between this species and other white oaks have not been reported from the state. The flowers bloom from April to May. BETULACEAE-BIRCH FAMILY Trees or shrubs; leaves alternate, simple, stipulate; flowers unisexual , the staminate usually in elongated, pendulous catkins, the pistillate pendulous or erect, short; sometimes woody; calyx in the staminate flowers 2- to 4-parted, absent in the pistilate flowers ; petals absent; stamens 2 or 4; ovary superior; ovule 1; fruit a nutlet subtended or leathery or woody bracts. The Betulaceae are made up of two genera and about 85 species found mostly in the Northern Hemisphere. Some botanists combine the Betulaceae with the Corylaceae, but there seem to be several Significant differences between the two families to justify their separation. KEY TO THE GENERA OF Betulaceae IN ILLINOIS 1. Bracts woody, persistent; leaves orbicular to obovate ______ 2. Alnus 1. Bracts leathery, deciduous; leaves ovate to oblong ________ 1. Betula 1. Betula [Tourn.] L. -Birch Trees or shrubs, often aromatic, the bark sometimes peeling into papery shreds; winter buds with many scales; leaves alternate, simple, toothed, stipulate; flowers unisexual, the staminate in elongated , pendulous catkins, the pistillate in short, erect spikes; staminate flowers 3 together, subtended by a bract, with a (2-) 4-toothed calyx, no petals, and 2 stamens; pistillate flowers 2-3 together, subtended by a 3-lobed bract, with no sepals and no petals, and with a sessile ovary with 2 styles; fruit a small, winged nut. Betula is a genus of 35 often attractive woody plants found in north temperate and arctic regions of both the Old and the New World. Many of the arctic species are dwarfed shrubs. Several species are grown as ornamentals. Five native species and two hybrids ocur in Illinois. Betula I 181 KEY TO THE TAXA OF Betula IN ILLINOIS 1. Leaves with 8 or more pairs of lateral veins ___________________ 2 1. Leaves with up to 7 (-8) pairs of lateral veins --________________ 3 2. Bark yellowish- or silvery-gray, peeling off in thin layers; leaves thin, green beneath _________________________ 1. B. alleghaniensis 2. Bark brownish to pinkish, peeling off in shaggy pieces; leaves firm, pale beneath ________________________________ 2. B. nigra 3. Bark peeling off in thin layers; small trees -------------------- 4 3. Bark close, not peeling off in thin layers; shruhs_~ ______________ 5 4. Leaves pubescent along the veins; most or all the fruiting spikes 3 cm long or longer ________________________ 3. B. p{lpyrifera 4. Leaves glabrous beneath; most or all the fruiting spikes less than 3 cm long _________________________________ 4. P. pOjJulifolia 5. Leaves acute to acuminate, some or all ovel' 3 cm long ___________ 6 5. Leaves obtuse to subacute, usually not more than 3 cm long ________ ___________________________________________ 7. B. pU1nila 6. Bark dark brown; fruiting spikes less than 1 cm thicL___________ _____________________________________ 5. B. X sandbergii 6. Bark gray; fruiting spikes at least 1 em thick ____ 6. B. X purpusii 1. Betula alleghaniensis Britt. Bull. Torrey Club 31: 166. 1904. Fig. 93. Betula lutea Michx. f. Arb, Am. 2:152. 1812, nomen illeg. Betula lutea Michx. f. var. macrolepis Fern. Rhodora 24:170. 1922. Betula alleghaniensis Britt. var. macrolepis (Fern.) Brayshaw, Can. Field-Nat. 80:161. 1966. Tree to 30 m tall (less in Illinois), with a trunk diameter up to 1. 2 m, with spreading, often pendulous branches; bark yellowish- or silvery-gray, becoming separated in thin scales rolled up on the edges; twigs at maturity brown and glabrous, the winter buds ovoid, acute, brown, up to 5 mm long; leaves thin, oblong-ovate to ovate, acute to acuminate at the apex, rounded at the sometimes asymmetrical base, sharply doubly serrate, dark green and dull on the upper surface, green beneath with pubescent veins, up to 10 cm long, up to 5 cm broad; petioles slender, hairy, up to 2 em long; staminate catkins usually 2-4 together, pendulous, up to 8 cm long, up to 6 mm thick, light brown; pistillate catkins sessile, erect, oblongoid , up to 3 cm long, becoming about as broad as long in fruit, the bracts up to 12 mm long, pubescent; nut oblongoid to ellipsoid, up to nearly 3 mm long, broader than its wings. 182 / SMARTWEEDS TO' HAZELNUTS " ,I...