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''Quercus havardii'' (common names include shinnery oak, shin oak and Havard oak) is a deciduous, low-growing, thicket-forming shrub that occupies some 2 to 3 million hectares in the southern Great Plains of North America. Clones may reach hundreds to thousands of years old, although aboveground stems typically live only 11 to 15 years. Shinnery oak stems are usually 1–2 m tall and codominate the plant community with mid- and tall-grasses which are usually taller than the oaks. The specific epithet honors U.S. Army surgeon and botanist Valery Havard, who contributed much to the knowledge of southwestern plants. The word "shinnery" seems to be derived from ''chêne'' (French for oak), and not from the height of the plant.〔(Oklahoma Biological Survey. ''Quercus havardii Rydb.'' )〕 ==Description== Form: A low shrub to 2 m or occasionally a small tree, ''Q. havardii'' forms large clonal thickets by extending rhizomes through the sandy soil where it is usually found. Rhizomes range from 3–15 cm in diameter and are concentrated in upper 60 cm of soil, although penetration depths of 9 m has been reported. Lateral roots and woody rhizomes are widespread near the soil surface. Ninety percent or more of shinnery oak's biomass is under ground, and fortuitous root grafting is common. These underground stems commonly spread to form plants 3 to 15 m or more in diameter. Single clones are reported to cover up to 81 ha and to achieve ages over 13,000 years.〔 Flowers: Shinnery oak is monoecious with both female and male flowers borne separately on the same plant.〔 Male catkins are densely flowered, 1.5-3.8 cm long, and hang downward. Female catkins are 3–7 mm long, contain 1 to 5 flowers, and are usually axillary on young shoots. Shinnery oaks are wind pollinated, and flowering occurs in the spring. Acorns: Acorns develop in 1 year, maturing in the autumn. Acorns occur alone or in clusters of 2 or 3, and are 12–25 mm long by 14–18 mm wide. A scaly cup covers about 1/3 to 1/2 of the nut. On average, acorn crops are produced in 3 out of 10 years.〔 Foliage: The leathery, highly variable leaves are grey green to olive green, have a lustrous upper surface, and are whitish and densely hairy below. Leaves are alternate, simple, with variable shape (oblong, ovate, or elliptical), and with wavy or shallowly lobed margins. Length is 2 to 8 cm and width 2 to 4 cm.〔 Twigs: Twigs are brown or grayish, 1-2.5 mm diameter, glabrous or densely covered with short grayish or yellowish hairs, that are lost with age. Buds are dark red-brown, somewhat spherical, about 2 mm long, and sparsely pubescent. Bark: Bark on the larger stems is light gray and scaly. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Quercus havardii」の詳細全文を読む スポンサード リンク
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