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Published In: A Natural Arrangement of British Plants 2: 222, 243. 1822. (10 Jan 1822) (Nat. Arr. Brit. Pl.) Name publication detail
 

Project Name Data (Last Modified On 8/26/2009)
Acceptance : Accepted
 

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BETULACEAE (Birch Family)

Contributed by Alan Whittemore

Plants trees or shrubs, monoecious. Leaves alternate, short- to less commonly long-petiolate. Leaf blades simple, pinnately veined, the margins toothed. Stipules scarious or somewhat hardened, broadly ovate, mostly shed during leaf development. Inflorescences of separate staminate and pistillate catkins (the pistillate ones in globose clusters in Corylus). Flowers actinomorphic, imperfect. Staminate flowers with calyces absent or of (1–)4(–6) minute, scalelike sepals; corollas absent; stamens mostly 4–6, with a reduced, nonfunctional pistil sometimes present. Pistillate flowers with calyces rudimentary or absent; corollas absent; stamens and staminodes absent; ovary inferior (but often appearing naked in the absence of perianth), with 2 locules toward the base but often appearing 1-locular toward the tip, the placentation axile. Styles 2 (sometimes united basally), each with a linear stigmatic region toward the tip. Fruits nuts, nutlets, or samaras, surrounded by bracts and often grouped into conelike infructescences. Six genera, 125–150 species, North America to South America, Europe, Asia.

Species of Betulaceae form an important part of the woody vegetation in many parts of Missouri. Many Betulaceae are tolerant of flooding and waterlogging, and they are a common component of the woody cover on stream banks and wet bottomlands. Other species dominate the woody understory in some Missouri forests. The seeds of all of our species are eaten by birds and other wildlife.

 

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1 1. Leaf blades with the tip broadly or bluntly pointed to shallowly notched; fruits in dense aggregates of 50120, separated by persistent woody bracts, the infructescence thus resembling a small woody cone; young growth (twigs, leaves, and inflorescences) sticky or resinous ... 1. ALNUS

Alnus
2 1. Leaf blades with the tip narrowed or tapered to a sharp point; fruits either in clusters of 5 or fewer, or if more per cluster then the bracts shed after flowering; young growth not sticky or resinous

3 2. Bark peeling in thin, papery sheets; undersurface of the leaf blade glaucous; fruits samaras 23 mm long, more or less hidden between overlapping bracts to form a smooth, conelike infructescence that disintegrates at maturity ... 2. BETULA

Betula
4 2. Bark smooth, ridged, grooved, or scaly, not peeling; undersurface of the leaf blade not glaucous; fruits nutlets or nuts 315 mm long, surrounded by bracts that do not overlap tightly, clustered or loosely overlapping to form an infructescence that is not smooth or conelike

5 3. Fruits spherical or depressed-spherical nuts 1015 mm long, in clusters of 13(5); leaf blades broadly ovate to broadly elliptic, with 69 veins on each side of the midrib ... 4. CORYLUS

Corylus
6 3. Fruits ovoid or flat-ovate nutlets (mostly 2 or 3 per flower), 26 mm long, in clusters of mostly 1025; leaf blades narrowly ovate or elliptic to obovate, with 1016 veins on each side of the midrib

7 4. Bracts lobed, relatively flat, and not surrounding the fruits; bark smooth ... 3. CARPINUS

Carpinus
8 4. Bracts unlobed, inflated, and surrounding the fruits; bark scaly ... 5. OSTRYA Ostrya
 
 
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