This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Shrubs or small trees, usually spiny, with alternate, simple, petioled, usually lobed leaves (those on the vegetative shoots generally of different shape than those of flowering branches and more deeply cut), deciduous stipules, and white (rarely pink) terminal corymbose flowers with early-deciduous bracts. Calyx-tube cup-shaped or campanulate, adnate to the carpels, its limb 5-lobed. Petals 5, spreading, rounded, inserted on the margin of the disk in the throat of the calyx. Stamens 5-25, inserted in 1-3 series; filaments filiform; anthers oblong, white, yellow, or red. Ovary inferior, or its summit free, 1-5-celled; styles 1-5, separate, persistent, usually surrounded at the base by tomentum; stigmas terminal; ovules 1 in each carpel, or if 2, dissimilar. Pome small, yellow, red, or rarely blue or black, containing 1-5 bony nutlets, each usually 1-seeded. Seed erect, flattish, the testa membranaceous. [Greek, strong, from the hardness and the toughness of the wood.]
About 300 species, natives of the north temperate zone, the tablelands of Mexico and the Andes; the center of distribution is in the eastern United States. Type species: Crataegus Oxya-cantlta L. The genus has been of great taxonomic interest for ten years, about 1000 species having been described, from the United States, during that period. Data are fast accumulating tending to show that many of these newly described species are hybrids.
A. Leaves not deltoid-cordate, pubescent or glabrous. a. Leaves pubescent or glabrous, if pubescent on one side only, always so beneath; thorns 1'-7' long (C. monogyna 3" long); fruit not black. * Petioles 1/2 inch or longer.
1. Leaves not deeply cut.
† Leaves cuneate, broadest at the middle or the apex.
Leaves broadest towards the apex.
Leaves not impressed-veined above, shining.
Leaves impressed-veined above, dull.
Leaves broadest at the middle.
Calyx-lobes usually deeply cut; nutlets deeply pitted on the ventral faces.
Calyx-lobes less deeply cut; nutlets with shallow pits on the ventral faces.
Leaves not impressed-veined.
Petioles usually glandless.
Calyx-lobes glandular-margined; fruit more than 4" thick; leaves not trilobate.
Calyx-lobes not glandular-margined; fruit 2"-4" thick; leaves often trilobate
towards the apex.
Petioles always glandular.
Petioles with small stalked glands.
Petioles with large, sessile glands.
†† Leaves broadest at the base.
Leaves 1/2'-2 1/2 long and wide, membranaceous; calyx-lobes usually entire.
Leaves blue-green, glabrous (except aspera); fruit hard at maturity
Leaves 1'-4' long and wide; calyx-lobes usually serrate.
2. Leaves deeply cut (only those of the vegetative shoots in C. spathulata).
Leaf-lobes sometimes 15: thorns 3"-9" long.
Leaf-lobes 3-7; thorns 1'-1 3/4'.
** Petioles about 1" long.
b. Leaves pubescent above, glabrous beneath; thorns 1/4'-1' long; fruit black.
B. Leaves conspicuously deltoid-cordate, glabrous.
Group I. Crus-galli. Leaves coriaceous, glandless; petioles 1/4'-3/4' long; corymbs many-flowered; calyx-lobes lanceolate-acuminate, usually entire; fruit red; calyx-tube flattened: flesh hard thin, greenish.
Leaves 3/4'-4' long.
Leaves 3/4'-2 1/2' long.
Leaves somewhat lobed.
Styles and nutlets usually 2.
Styles and nutlets usually 3-5.
Lobes of the leaves irregular, obtuse.
Vegetative leaves oblong.
Vegetative leaves round.
Lobes of the leaves regular, acute; calyx-lobes serrate.
Group II. Punctatae. Leaves subcoriaceous; petioles 1/4' - 1/2' long; corymbs many-flowered; calyx-lobes lanceolate-acuminate, usually entire; flesh of fruit hard, thick; calyx-tube usually flattened.
* Written by Mr. W. W. Eggleston.
Fruit glabrous; calyx-lobes entire.
Fruit ellipsoidal; nutlets usually 3 or 4.
Leaves bright yellow-green, slightly impressed-veined above; fruit ellipsoidal.
Leaves dull gray-green, strongly impressed-veined above; fruit short-ellipsoidal.
Leaves obovaie, narrow.
Leaves oblong, broad.
Nutlets 2 or 3.
Nutlets 4 or 5.
Fruit villous; calyx-lobes glandular-serrate.
Leaves rhombic-elliptic; petioles 1/4'-3/4' long; corymbs many-flowered, pubescent; calyx-lobes lanceolate, acuminate, glandular-laciniate, villous; fruit red, its flesh glutinous; calyx-lobes reflexed.
Leaves dark green, glabrous and shining above, coriaceous.
Fruit sometimes 8" thick; stamens usually 10; leaves and anthers large.
Fruit sometimes 6" thick; leaves and anthers small; stamens 15-20.
Leaves gray-green, pubescent and dull above, subcoriaceous.
Leaves rhombic-ovate, lobed.
Leaves oval, more entire.
Group IV. Brainerdianae (Anomaiae). Leaves elliptic to ovate, subcoriaceous to membranous; petioles 1/2'-1 1/2' long; corymbs many-flowered; calyx-lobes lanceolate-acuminate, glandular-serrate; fruit red; calyx-lobes reflexed; flesh
thin, succulent or glutinous.
Fruit and corymbs pubescent; calyx-lobes sharply glandular-serrate.
Leaves serrate; styles and nutlets 2 or 3.
Leaves dentate; styles and nutlets 4 or 5.
Fruit and corymbs glabrous; calyx-lobes remotely glandular-serrate.
Group V. ROTUNDIFOLIAE.
Leaves elliptic-ovate to orbicular; subcoriaceous; petioles 1/4'-2' long; young foliage usually yellow-green; corymbs many-flowered; calyx-lobes usually lanceolate-acuminate; fruit red, the flesh soft; calyx-lobes reflexed.
Leaves longer than wide.
Leaves of about the same length and breadth.
Leaf-lobes acute or obtuse.
Calyx-tube prominent; fruit subglobose.
Leaves acutely lobed toward the apex; calyx-lobes glandular-laciniate.
Leaves not acutely lobed; calyx-lobes glandular-margined only.
Fruit pyriform, yellow-red; flowers and fruit maturing early.
Fruit globose, red; flowers 3 or 4 days later.
Fruit round in cross-section, 3" - 5" thick.
Fruit angular in cross-section, s"-8" thick.
Group VI. Virides. Leaves oblong-ovate to oval; membranous, dark green, shining and glabrous above; petioles 1/4'-1 1/4' long; corymbs many-flowered; calyx-lobes entire; fruit red, glabrous; flesh hard, edible.
Leaves ovate; lobes shallow; fruit yellow-red.
Leaves oblong-ovate; lobes deep.
Fruit bright red, glaucous, 2" or 3" thick; leaves serrate.
Fruit dull dark red, 3" or 4" thick; leaves coarsely serrate.
Group VII. Intricatae. Leaves elliptic to ovate, subcoriaceous, the teeth gland-tipped; petioles 1/4'- 1 1/4' long; young foliage usually yellow-green; corymbs 3-7-flowered; bracts glandular, very deciduous; calyx-lobes lanceolate-acuminate, generally strongly toothed toward the apex; fruit greenish-yellow to reddish-brown, bluntly angular; calyx-tube prominent, the lobes reflexed; flesh hard, thick.
Foliage and fruit pubescent; corymbs villous.
Fruit globose, greenish- to reddish-brown.
Fruit ellipsoid or pyriform, yellow.
Foliage, corymbs and fruit glabrous.
Leaves entire or the lobes crenate.
Leaves lobed, the lobes acute.
Leaves elliptic-ovate; fruit pyriform-ellipsoidal; anthers small.
Leaves ovate to oval; fruit globose or subglobose; anthers large.
Fruit red-green to red-brown.
Group VIII. Flavae.
Leaves short-obovate to spatulate, membranous; petioles 1/4'-3/4' long; corymbs few-flowered; calyx-lobes glandular-serrate; fruit green to orange or red; calyx-tube prominent, the lobes reflexed; flesh usually soft at maturity. Shrubs and trees of the sandy pinelands of the southern coastal plain; only one, of the several species, reaching southern Virginia.
Easily recognized by the zigzag branches and very glandular foliage. 39. C. flava.
Group IX. Tenuifoliae.
Leaves ovate, membranous, often slightly pubescent; petioles slender, 1/2'-1 1/4' long; young foliage usually bronze-green; corymbs many-flowered; fruit red, glabrous; calyx-lobes erect or spreading, persistent;flesh succulent.
Fruit ellipsoid, ovoid or pyriform.
Fruit small, 3" or 4" thick, with rather firm flesh; leaves much lobed.
Fruit large, 5"-9" thick, with soft flesh; leaves not conspicuously lobed.
Fruit compressed-globose or subglobose.
Lobes of the leaves reflexed.
Lobes of the leaves spreading or ascending.
Terminal leaves cuneate.
Terminal leaves cordate.
Group X. Pruinosae.
Leaves ovate, membranous to subcoriaceous, blue-green, glabrous (except C. aspera); petioles 1/4'-1 1/4' long; young foliage usually bronze-green; corymbs many-flowered; calyx-lobes deltoid-acuminate; fruit pruinose; calyx-tube prominent, the lobes spreading, persistent.
Leaves usually cordate.
Fruit conspicuously angled, strongly pruinose.
Fruit without conspicuous angles, slightly pruinose.
Leaves usually cuneate.
Lobes of the leaves deep, acuminate.
Lobes of the leaves shallow, acute.
Fruit without conspicuous angles.
Fruit conspicuously angled.
Leaves 1 1/2'-3 1/2' long, 1 1/4'-2 3/4' wide.
Leaves not more than 2 1/2' long, 2 1/2' wide.
Group XI Coccineae (Molles).
Leaves ovate, membranous to subcoriaceous; petioles 3/4'-1 1/2' long; corymbs many-flowered; calyx-lobes glandular-serrate; fruit usually red and pubescent; calyx-lobes swollen, erect or spreading; flesh thick, soft, edible. Mature leaves usually elabrous above: voung foliaere bronze green: anthers pink.
Leaves sharply lobed; eastern.
Corymbs nearly glabrous; lobes reflexed.
Corymbs very pubescent; lobes ascending.
Leaves subentire; southwestern.
Corymbs and fruit nearly glabrous.
Corymbs and fruit very tomentose.
Leaves broadly ovate.
Corymbs and fruit glabrous; stamens about 20.
Corymbs and fruit pubescent or tomentose.
Leaves on vegetative shoots cuneate.
Leaves concave, 1 1/4'-2 3/4' long, 1 wide.
Leaves plane, 1 1/4'-4' long, 1 1/4'-3 1/2' wide.
Leaves on vegetative shoots cordate.
Mature leaves tomentose above; young foliage yellow-green; anthers yellow.
Leaves on vegetative shoots cuneate at base.
Lobes of the leaves broad, shallow, acuminate.
Lobes narrow, deep, acute.
Fruit globose; calyx-tube rather prominent; leaves subcoriaceous.
Fruit ellipsoidal-pyriform; calyx-tube obscure; leaves membranous.
Leaves on vegetative shoots cordate.
Group XII. OXYACANTHAE.
Leaves ovate, 3-15-lobed or cleft; corymbs many-flowered; fruit red, styles and nutlets 1; introduced species. 68. C. monogyna.
Group XIII. MlCROCARPAE.
Leaves membranous, lobed; flowers small; stamens about 20; fruit small, red. Shrubs or trees of the South, with grayish-brown scaly and warty bark.
Leaves deeply lobed or cut; styles and nutlets 2.
Leaves of the vegetative shoots only, lobed, the other leaves spatulate; styles and nutlets 5.
Group XIV. Parvifoliae.
Leaves small, subcoriaceous; corymbs 1-3-flowered. Shrubs.
Group XV. Douglasianae.
Leaves subcoriaceous; petioles 1/4'-3/4' long; corymbs many-flowered; nutlets roughly pitted on the ventral faces. 72. C. Douglasii.
Group XVI. Cordatae.
Leaves often conspicuously 3-5-lobed; petioles 1/2'-2' long; corymbs many-flowered; fruit small, scarlet; nutlets bare at the apex. 73. C. Phaenopyrum.