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Key to families | Table of families and genera

Specimen numbers are hyperlinked to records in the Consortium of California Herbaria data view where possible. Taxa are hyperlinked to entries in the Jepson Interchange via the "[Online Interchange]" link.

 

BETULACEAE BIRCH FAMILY

John O. Sawyer, Jr.


Shrub, tree; monoecious. Stem: trunk < 35 m; bark smooth to scaly, peeling in thin layers or not, lenticels present or not. Leaf: simple, alternate, petioled, deciduous; stipules deciduous; blade ovate to elliptic, generally serrate, generally ± doubly so. Inflorescence: catkin, generally appearing before leaves, often clustered; bracts each subtending 2–3 flowers, 3–6 bractlets. Staminate inflorescence: pendent, ± elongate. Pistillate inflorescence: pendent or erect, developing variously in fruit (see key to genera). Staminate flower: sepals 0–4, minute; petals 0; stamens 1–10; pistil vestigial or 0. Pistillate flower: sepals 0–4; petals 0; stamens 0; pistil 1, ovary inferior or superior, chambers 2, each 1-ovuled by abortion, stigmas 2. Fruit: achene, nut, winged or not, subtended or enclosed by 1–2 bracts.
6 genera, 155 species: generally northern hemisphere; some cultivated. [Furlow 1997 FNANM 3:507–538] —Scientific Editor: Thomas J. Rosatti.

Key to Betulaceae

1. Leaf base oblique-cordate; fruits 1–2 per catkin, not winged, each enclosed in a papery involucre of 2 fused bracts; pistillate calyx present, ovary inferior ..... CORYLUS

1' Leaf base subcordate, rounded, ± truncate, or tapered; fruits many per catkin, winged, each subtended but not enclosed by 1 bract; pistillate calyx 0, ovary superior

2. Pistillate catkin cone-like, with woody bracts remaining attached after fruit release ..... ALNUS

2' Pistillate catkin not cone-like, with papery, lobed bracts released with but not attached to fruit ..... BETULA

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Citation for the whole project: Jepson Flora Project (eds.) [year] Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html [accessed on month, day, year]
Citation for an individual treatment: [Author of taxon treatment] [year]. [Taxon name] in Jepson Flora Project (eds.) Jepson eFlora, [URL for treatment]. Accessed on [month, day, year].
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