Betulaceae - birch family
Leaves of the birch family are simple and arranged alternately on the stem. Some species have spur shoots (also called short shoots) that grow very little each year, and on these shoots leaves can appear, without close inspection, to be opposite each other. Leaves are doubly serrate, a feature more evident in some species than in others. They are pinnately veined; that is, they have a primary vein, sometimes called a midrib, that runs the length of the leaf blade and secondary veins branching from it along its entire length.
Flowers are unisexual; that is, each flower is either staminate (with stamens bearing pollen) or carpellate (with pistils containing ovules that develop into seeds). Because both kinds of flowers are found on the same tree/shrub, the plants are called monoecious (moe-NEE-shus), from the Greek monos (single) and oikos (house). Staminate flowers plus bracts are aggregated in what is called an ament, specifically a staminate ament. These aments are formed in the fall (except in the genus Carpinus), and with the warmer weather in the spring they become pendant and the pollen is shed. This happens before leaves emerge from the buds because species of the birch family are wind pollinated. Carpellate flowers plus bracts are also aggregated in aments, called carpellate or pistillate aments, but these aments do not become pendulous in the spring and also they differ among species much more than staminate aments. For example, in the genus Betula (birch) a carpellate ament with fully developed seeds falls to pieces, dispersing both seeds and bracts. In alders (Alnus), however, the carpellate aments remain intact on the twigs following seed dispersal and, with their bracts now having become almost "woody", they have a cone-like appearance.

Mount Desert Island is home to 9 species and 1 hybrid in 5 genera that grow without cultivation. (There are only 6 genera of Betulaceae worldwide; Ostryopsis grows in eastern Asia.) Click on a link below or scroll down for more information.
   Alnus (2 species)
      Alnus incana - speckled alder (common [see note 1 below])
      Alnus viridis - green alder (common)
   Betula (4 species and 1 hybrid)
      Betula alleghaniensis - yellow birch (common)
      Betula x caerulea - blue birch (occasional)
      Betula cordifolia - mountain paper birch) (occasional)
      Betula papyrifera - paper birch (common)
      Betula populifolia - gray birch (common)
   Carpinus (1 species)
      Carpinus caroliniana ssp. virginiana - American hornbeam (rare)
   Corylus (1 species)
      Corylus cornuta - beaked hazelnut (common)
   Ostrya (1 species)
      Ostrya virginiana - eastern hophornbeam (occasional)

Alnus (alder)
The word alnus (lowercase) was the name used by the ancient Romans for an alder and for objects made of its wood. Alnus, beginning with an uppercase A, is now the scientific name for the genus. Of the three species of alder in Maine, two grow on Mount Desert Island. The third species, Alnus serrulata (smooth alder), grows in southern Maine and is known to hybridize with Alnus incana (speckled alder). There is, however, no report of hybridization between MDI's two alder species, undoubtedly because their times of shedding pollen do not overlap; speckled alder has finished shedding its pollen well before green alder begins. Both pictures below were taken on 18 April 2008, clearly showing the difference in development between the two species. Observations are reported below under each species.
   Distinguishing between MDI's two alders in the winter is relatively straightforward. The buds of speckled alder (below left) are clearly stalked (vs. sessile or with a stalk no more than 1 mm long for green alder, below right), rounded at the apex (vs. acute [pointed] for green alder), scurfy-pubescent (vs. glabrous for green alder), and brownish (vs. reddish for green alder).

 

Alnus incana (speckled alder) is a species generally of low, wet areas on MDI. Although the specific epithet incana means gray or hoary, the common name speckled likely refers to the light-colored lenticels that stand out against the darker bark. Like other members of the wind-pollinated birch family, pollen is shed early in the season, before leaves have expanded. Following is a record of observations during 2008.
   6 April 2008 - along Park Loop Road, near precipice: "shedding of speckled alder pollen" (JW)
   8 April 2008 - intersection of road between Route 3 and Park Loop Road with road leading to Sieur de Monts: two trees shedding pollen and with carpellate flowers open (TFV)
   9 April 2008 - woods road off Route 102, just north of intersection of 102 and southern end of Cape Road: Alnus incana shedding pollen (TFV)
   25 April 2008 - pollen shed apparently completed, at least at lower elevations (TFV)

Alnus viridis (green alder) tends to grow in somewhat drier areas than A. incana.
   9 April 2008 - woods road off Route 102, just north of intersection of 102 and southern end of Cape Road: not close to shedding pollen; the staminate aments stiff and unexpanded. (TFV)
   25 April 2008 - southern half of Breakneck Road: no sign of pollen shed (TFV)
   21 May 2008 - Big Moose Road (Bass Harbor): pollen shed completed (TFV)

Betula (birch), the name of the genus, comes from betulla (with a double l), used by ancient Romans (e.g., Pliny in his discussion of aboriculture in book XVI of his Natural History [16:74, 176, and 209 in the Loeb Classical Library edition]) for the birch tree (Latin Oxford Dictionary). Bark on mature trees is distinctive, white (and exfoliating in some species) or golden.

Betula alleghaniensis (yellow birch) The bark (at right) of yellow birch is a yellowish brown and separates in curls (vs. sheets of paper birch). If you scratch a twig (deep enough to see its light-colored inner portion), you will smell a wintergreen odor. This is the only birch on MDI that has this smell.

Betula x caerulea (blue birch)

Betula cordifolia (heart-leaved paper birch)

Betula papyrifera (paper birch) bark of younger tree (near right) and bark of older tree (far right)

Betula populifolia (gray birch) means the birch with poplar-like leaves. The leaves of two common poplars, Populus tremuloides (quaking poplar, commonly called quaking aspen) and Populus grandidentata (big-toothed poplar or big-toothed aspen), flutter noticeably in even relatively little air movement, a result of their petioles (that is, leaf stalks) being flat. Now, the leaf petioles of gray birch aren't flat, but they are long enough for the movement of the leaves in a slight breeze to resemble that of the poplars mentioned above.    Gray birch leaves (image at right) are quite triangular, with a long, tapered apex. An easy way to remember the name gray birch is to note that the leaves resemble, with a little imagination, a front view of the head of an elephant (the tapering leaf apex being the trunk), a gray animal.

The preformed (i.e., in the fall) staminate aments of Betula populifolia (see image at right) usually grow singly and are much thinner than those of B. papyrifera.

Carpinus (hornbeam)

Carpinus caroliniana (American hornbeam)

Corylus (hazelnut)
The word corylus (lowercase) was used by the ancient Romans (e.g., Pliny in his discussion of aboriculture in book XVII of his Natural History [17:67 in the Loeb Classical Library edition]) for the "hazel-tree" (Oxford Latin Dictionary).

Corylus cornuta (beaked hazelnut). Both the specific epithet cornuta, an adjective meaning horned, and the English adjective beaked refer to the prolonged husk (bracts greatly expanded and fused during fruit development) that encloses the nut. This nut, sometimes called a filbert, is sweet and edible, a fact that has not been lost on squirrels, who tend to be much more proficient than humans at collecting them.
18 April 2008 - Great Meadow loop: "in flower ... magenta stigmas and males shedding pollen" (JW)

Ostrya (hop-hornbeam)
The genus name Ostrya comes from a Greek tree mentioned by Pliny in a brief discussion of infelicia ligna, translated as "unlucky wood" in the Loeb Classical Library edition of his Natural History (13:116-117), in which he describes the wood of a Greek tree "named the ostrys, another form of the name being ostrya," as being "hard and solid". Pliny goes on to report that "it is said that if it is brought into a house[,] it causes difficulty in child-birth and painful deaths."

Ostrya virginiana (eastern hop-hornbeam), the sole member of the genus on Mount Desert Island (and the only Ostrya species with any sizable range in North America), has very hard wood and thus was used at some point for tool handles. The image at the right shows the distinctive so-called "cat-scratch" bark.

Note:
   1. Frequency designations are from the paper "Vascular flora of the Acadia National Park region, Maine" by Craig W. Greene, Linda L. Gregory, Glen H. Mittelhauser, Sally C. Rooney, and Jill E. Weber, published in the spring 2005 issue (vol. 107, No. 930) of Rhodora: Journal of the New England Botanical Club.

Thank you to the following champlainers for their observations:
   TFV = Thomas F. Vining
   JW = Jill Weber