ÀCER. The Maples.

Trees with terete branches; scaly buds; long petioled, opposite leaves; fruit consists of two long-winged samaras which are joined at their base, separating at maturity. The sap of some of the species, when concentrated, yields the maple sugar and sirup of commerce.

1. Acer NegÚndo LinnÆus. Box Elder. Plate 111. A medium-sized tree with a short trunk and round head; bark of young trees smooth and gray, becoming thick on old trees, light to dark brown and more or less furrowed or rarely somewhat flaky; twigs smooth and greenish; leaves of average size are 1.5-3 dm. long, generally with 3 leaflets on the flowering branches, sometimes 5 or rarely with 7, on sterile branches or on growing shoots 3-7, the petioles generally ¹/₃-¹/₂ the length of the leaf and glabrous or nearly so at maturity; leaflets all on stalks more or less pubescent, the lateral stalks short, the terminal ones much longer, leaflets of varying size and shape, the margins usually varying from lobed to serrate or entire, pinnately veined, smooth above at maturity and remaining more or less pubescent beneath, especially along the veins; flowers appear just before the leaves the last of April or the first of May, the staminate and pistillate on separate trees; fruit matures late in summer, the body of the samara green and more or less pubescent.

Distribution.—New England to Florida, west to Minnesota and south to eastern Texas. In Indiana, it is found throughout the State in moist or wet places along creeks and rivers, and infrequently on the highlands along roadsides and fences. Its original distribution in the State can only be conjectured. Judging from its tolerance to shade and its habitat, and from the earliest reports of its occurrence in the State, this species was quite rare in the northern part of the State, becoming infrequent to frequent in its habitat in the southern part of the State. Even today it is rather local in its distribution. I have never seen it on the low mucky border of a lake.

Remarks.—This species on account of its rapid growth was formerly much used in our area as a shade tree. It is believed that most of the trees now found along roadsides, fences, clearings and on the drier banks of streams are from seed distributed by the wind from planted trees. This species is now little used as a shade tree and is never recommended because it sheds its leaves early, and is subject to injury from disease and insects.

Plate 111

1a. Acer Negundo variety violÀceum Kirchner. (Rulac Nuttallii Nieuwland). This variety is distinguished by its glaucous twigs and by the body of the fruit being glabrous at maturity. In most instances when the bloom is rubbed from the twigs they show a purple tinge, hence the varietal name.

Distribution.—I have this variety in Indiana from the following counties: Brown, Cass, Elkhart, Franklin, Fulton, Hendricks, Henry, Jennings, Lagrange, Martin, Posey, St. Joseph, Vermillion and Wayne.2. Acer saccharÌnum LinnÆus. Silver Maple. Soft Maple. White Maple. Plate 112. Medium sized trees; bark of small trees smooth and gray, becoming on old trees reddish-brown, and freely splitting into thin scales; branchlets light to reddish-brown and generally turning upward at their tips; leaves generally about 1 dm. long, generally somewhat cordate at the base, sometimes truncate, deeply 3-lobed, each of the lateral lobes with an additional lobe below, margins of all of the lobes more or less irregular or even lobed, the two principal sinuses generally show a tendency to close, leaves hairy beneath when young, glabrous above and below at maturity and very glaucous beneath; flowers appear in March or April in the axils of the leaves of the previous year, the staminate and pistillate in separate clusters on the same or different trees; fruit on pedicels 1.5-6 cm. long, maturing in the spring or early summer, green, densely hairy while young and remaining more or less hairy at maturity, 4-7 cm. long, wings 1-2 cm. wide.

Distribution.—New Brunswick to Florida, west to South Dakota and south to Texas. Locally frequent to very common in all parts of Indiana. This species is always found in wet or moist places, and in the lower Wabash bottoms in low overflow lands or in or about old sloughs it often forms the principal stand. It is more frequently associated with black willow, white elm, red birch, sycamore, etc.

Remarks.—The silver maple has been used extensively for shade tree planting. The branches are very brittle, and ice storms sometimes break off so many branches that the tree may be badly injured. The shade trees of this species are in many parts of the state being killed by scale insects, and for this reason it should not be used. On account of its rapid growth it has also been much used for windbreaks but this practice should be discouraged and better species used.

Plate 112

3. Acer rÙbrum LinnÆus. Red Maple. Soft Maple. Swamp Maple. Plate 113. Medium to large sized trees; bark of small trees smooth and gray, becoming dark brown on old trees, somewhat furrowed and scaly; branchlets smooth and reddish; twigs generally smooth but sometimes hairy, becoming glabrous by autumn; leaves 5-12 cm. long, 3-5 lobed, more or less cordate at the base, sometimes truncate or rounded, sinuses acute, those of 3-lobed leaves generally wider angled than those of 5-lobed ones, the lobes more or less irregularly serrate or dentate, hairy while young, glabrous above and more or less hairy beneath at maturity, glaucous beneath; flowering period March or April; flowers red or reddish, in the axils of the leaves of the previous year, the staminate and pistillate in separate clusters on the same or different trees; fruit maturing late in spring, on pedicels 3-8 cm. long, generally red, sometimes green, glabrous at maturity, rarely somewhat pubescent, 1.5-3.5 cm. long.

Distribution.—Newfoundland to Florida, west to Minnesota and south to Texas. It is found in all parts of Indiana. Its preferred habitat is that of low ground about lakes, swamps, along streams and in the "flats" in the southeast part of the State. Throughout its range in Indiana where it is found in low ground, it is in places rich in organic matter, except in the "flats" of the southern part of the State where it grows in a hard clay soil with sweet gum, red birch, etc. In contrast the silver maple is generally found growing in wet places with little organic matter; especially is this true in the lower Wabash bottoms. The red maple grows also on high ground. In the northern part of the State it is only an occasional tree of gravelly ridges or on high ground about lakes or along streams. In the southern part of the State it is a local to a frequent tree in most parts of the "knob" area where it is associated with white oak, black oak, black gum, etc. It is also an occasional tree on the top of bluffs and cliffs.

Remarks.—The red maple is not abundant enough in Indiana to be of any economic importance. It grows rapidly and should replace the silver maple for shade tree planting since its branches are not broken off as easily by ice storms and it is more resistant to insect attack.3a. Acer rubrum variety DrummÓndii (Hooker and Arnott) Torrey and Gray. This variety of the red maple is a form found in the dense swamps of the lower Wabash Valley. It is distinguished from the type by its twigs which generally remain more or less hairy until maturity; by the under surface of the leaves remaining more or less tomentose during the summer, and by its larger fruit. This variety is known with certainty only from Little Cypress Swamp in Knox County about 12 miles southwest of Decker. Here it is a frequent to a common tree associated with cypress, swell-butt ash, button-bush, sweet gum, etc. All of the trees of this locality have 5-lobed leaves.

Plate 113

A specimen collected in the "bottoms" about two miles east of Huntingburg in Dubois County has 3-lobed leaves which are tomentose beneath at fruiting time and has fruit intermediate in size between the type and variety Drummondii which I doubtfully refer to variety tridens Wood.4. Acer nÌgrum F. A. Michaux. Black Maple. Black Sugar. Plate 114. Medium to large sized trees with dark furrowed bark on old trees; leaves a little wider than long, 6-15 cm. long, on petioles usually 3-15 cm. long which are more or less swollen at the base and by maturity develop a scale like appendage on each side of the petiole at the base—especially on each of the terminal pair of leaves, sometimes with foliar stipules which are 2-3 cm. long on stalks of equal length, leaves with three main lobes, the two lower lobes generally have a small lobe at their base, margins of lobes entire and undulating, sinuses between main lobes generally rounded at the base, wide and shallow, base with a narrow sinus, the lower lobes often overlapping, rarely somewhat dentate, dark green above and a paler yellow green below, hairy on both surfaces when young, becoming at maturity glabrous above and remaining more or less pubescent beneath; flowers appear in May when the leaves are about half grown on long hairy pedicels, the staminate and pistillate in separate clusters on the same or different trees; fruit matures in autumn, the samaras about 3 cm. long.

Distribution.—Quebec to Georgia, west to South Dakota and south to Louisiana. Found in all parts of Indiana and invariably associated with sugar maple, and often with beech in addition. Frequently almost pure stands of sugar maple may be found with the black maple absent. Where found it is usually a frequent to common tree, and when it occurs on a wooded slope it is more frequent near the base and appears to be able to advance farther into moist situations than its congener.

Remarks.—This tree cannot be distinguished from the sugar maple by its form, but at short range can be separated from it by its richer green foliage and by the drooping habit of the lower lobes of the leaves. It is commonly separated from the sugar maple by the darker color and by the narrower and shallower furrows of the bark, but these characters will not always separate the two species. Hence, when buying black maple trees from a nurseryman you may receive the sugar maple. Those who distinguish the two species agree that the black maple is the more desirable tree for shade tree planting. The black and sugar maple are the two most desirable trees for shade tree planting in Indiana. They are long lived, have a very desirable form, beautiful foliage, a long leaf period, and are quite free from disease and insect injury.

Plate 114

5. Acer sÁccharum Marshall. Sugar Maple. Sugar Tree. Hard Maple. Rock Maple. Plate 115. Usually large, tall trees. The bark of small trees is smooth or rough, becoming fissured on old trees, tight or on very old trees sometimes the ridges loosen on one edge and turn outward. The leaves are extremely variable on different trees, and frequently show a wide variation on the same tree, as to form and in the presence or absence of hairs on the petioles and on the under surface of the leaves. In our area all of the forms which have the majority of the leaves longer than wide or about as wide as long, may be considered as falling within the type. The average sized leaves are 6-12 cm. long, 3-5 lobed, more or less cordate at the base, generally with a broad sinus, sometimes truncate or slightly wedge-shape, sinuses generally wide-angled and rounded at the base, sometimes acute, hairy beneath when young, becoming smooth at maturity except for a few hairs along the veins or in the main axils of the veins, or sometimes remaining more or less pubescent over the whole under surface, more or less glaucous beneath; flowers appear in April or May, on hairy pedicels 3-7 cm. long, the staminate and pistillate in clusters on the same or different trees; fruit ripening in autumn, samaras glabrous and usually 2-4 cm. long.

Distribution.—Newfoundland to Georgia, west to Manitoba and south to Texas. A frequent to a very common tree in all parts of Indiana. It is confined to rich uplands, or along streams in well drained alluvial soil. Throughout our area it is constantly associated with the beech. It is absent in the "flats" of the southeastern part of the State, and on the crest of the ridges of the "knob" area of Indiana, but it is a frequent or common tree on the lower slopes of the spurs of the "knobs."

Remarks.—The under surface of the leaves of the sugar maple in the northern part of its range are green, while those of the southern part of its range are quite glaucous beneath. To distinguish these two intergrading forms the southern form has been called Acer saccharum var. glaucum Sargent[61]. All of the trees seen in Indiana have leaves more or less glaucous beneath. This character, however, is not always evident in dried specimens. The writer prefers not to apply the varietal name to the forms of our area. The sugar maple always has been and will continue to be one of the most important trees of the State. In its mass distribution in Indiana it ranks not less than third. In the quality and uses of its wood it is equalled or exceeded only by the oak, ash and hickory. When compared with white oak it is a little lighter but thirty per cent stronger and fifty-three per cent stiffer. The greatest amount of the annual cut of maple is worked into flooring which is shipped to all parts of the world. It is much used in the manufacture of furniture and ranks third in use for veneer and hard wood distillation, and as a fuel wood is excelled only by hickory. Since pioneer times, the sap of this tree has been made into sirup and sugar and their manufacture now forms a valuable industry. On an average it takes 3 to 4 gallons of sap to make a pound of sugar, and an average sized tree will annually yield about 3 to 4 pounds of sugar.

Plate 115

The sugar maple on account of its slow growth has not been used much in reforestation. It is very tolerant of shade, can adapt itself to almost all kinds of soils, thrives either in a pure or mixed stand, and is practically free from injury of insects and diseases. It has, however, been extensively used as a shade tree. For this purpose it is scarcely excelled by any other tree. When grown in the open it almost invariably assumes a symmetrical oval form, and the autumnal coloration of its foliage is rarely surpassed by any of our trees. Where a large tree is desired for street or ornamental planting the sugar maple can safely be recommended.5a. Acer saccharum variety RugÉlii (Pax) Rehder. This variety of the sugar maple has leaves much wider than long, smaller and 3-lobed. The lobes are long acuminate and usually entire, sometimes the lower lobe has a small lobe near the base. This variety is included in our flora on the authority of C. S. Sargent who has given this name to specimens from Indiana in the writer's herbarium. The specimens so named are from the southern part of the State. While there is a wide range of difference in the shape of the leaves of the typical 5-lobed Acer saccharum and its variety Rugelii, all intermediate forms can be easily found. The leaves of a tree will vary most on those trees whose average shaped leaves are farthest from the typical form.5b. Acer saccharum variety SchnÉckii Rehder. This variety in its extreme form is well marked by having the petioles and under surface of the leaves densely covered with hairs. The variety is characterized by having a "fulvous pubescence," but the 18 specimens at hand show the color of the pubescence on both young and mature specimens to range from white to fulvous. The leaves of all specimens at hand are 5-lobed and show a variation of leaves with petioles and under surface of leaves densely pubescent to those with petioles glabrous and with densely pubescent under surface. The habitat is that of a dry soil and associated with beech. It has been found in Gibson, Martin, Perry, Posey and Vanderburgh counties.