Crataegus
L. (hawthorn).
Contributed by James B. Phipps
Plants shrubs or
small trees. Trunks sometimes armed with simple or branched thorns. Branches
often producing straight to slightly curved thorns, these usually determinate,
persistent for a few years, rarely becoming elongated or leafy. Bark various
shades of tan to orangish brown and brown, appearing mottled or checkered,
usually peeling in irregular flakes or thin patches, in a few species not
flaking, but instead tight and furrowed. Twigs brown to dark brown, becoming
gray or grayish brown with age, glabrous or hairy. Winter buds terminal and
lateral, small, broadly ovoid to nearly globose, with few to several
overlapping scales, these dark red, somewhat fleshy, glabrous. Leaves
deciduous, alternate but sometimes appearing clustered at the tips of short
branchlets, folded during development, mostly short- to long-petiolate, the
petioles grooved on the upper surface, with or without glands along the
margins. Stipules relatively large and persistent on rapidly elongating shoots,
smaller and shed early on flowering branches, membranous or more commonly leafy,
the margins with gland-tipped teeth. Leaf blades simple, those of rapidly
elongating branches often larger and more deeply lobed, those of flowering
branches smaller, unlobed or lobed, variously shaped, the margins bluntly or
sharply and finely to coarsely toothed, the teeth sometimes gland-tipped, the
surfaces glabrous or variously hairy at maturity, the upper surface lacking
glands. Inflorescences appearing terminal on lateral, short branchlets,
dome-shaped to more or less flat-topped, small panicles of several to numerous
short- to long-stalked flowers, occasionally reduced to umbellate clusters or
solitary flowers, produced as the leaves develop or later, the axis and stalks
glabrous, hairy, or stalked-glandular, the stalks each with a small bract at the
base, this linear to narrowly oblong-elliptic, membranous to subherbaceous,
usually gland-toothed along the margins, often shed early. Flowers epigynous,
usually malodorous, the hypanthium fused to the ovaries, globose or slightly
urn-shaped, with a greenish yellow nectar disc at the mouth (this usually
turning red after pollination has occurred), glabrous or hairy. Sepals 5,
spreading to somewhat reflexed at flowering, mostly triangular to narrowly
triangular, angled or tapered to a sharply pointed tip, the margins entire to
toothed or shallowly lobed, the teeth or lobes gland-tipped, the outer surface
glabrous or hairy, persistent until fruiting or shed after flowering. Petals 5,
broadly obovate-elliptic to nearly circular, usually slightly concave (cupped)
at flowering, the margins entire or sometimes slightly uneven, white or less
commonly pinkish-tinged at flowering, usually pinkish-tinged in bud, fading to
white with age, overlapping in bud. Stamens (5–)10–20(–25), the filaments often
somewhat unequal in length, attached to the margin of the nectar disc, the
anthers (0.3–)0.5–1.0(–1.8) mm, ivory to cream-colored or pink to red, rarely
dark pinkish purple. Pistil 1 per flower, of (1–)2–5 fused carpels. Ovary
inferior, sometimes protruding slightly from the hypanthium at flowering, with
(1–)2–5 locules, each with usually 2 ovules (but 1 of these usually abortive).
Styles (1–)2–5, free or fused at the base, exserted from the hypanthium, the
stigmas club-shaped. Fruits pomes, globose or broadly ellipsoid, glabrous or
hairy at maturity, dark to bright red to less commonly orange or yellow, the
surface sometimes dotted, with (1–)2–5 stones (usually called nutlets in Crataegus),
these hard or bony, wedge-shaped when more than 2, dorsally usually slightly
concave or shallowly grooved, indehiscent, 1(2)-seeded, embedded in the fleshy
to mealy middle layer of the fruit. About 200 species, most diverse in
temperate regions of the northern hemisphere, a few in the montane tropics and
temperate southern hemisphere..
Where abundant,
hawthorns are important wildlife plants, providing shelter and protection for
numerous small mammals, excellent nesting sites for birds, and autumnal food
for medium-sized passerine birds, ground-birds, rodents, deer, cattle, and even
bears. Cattle and deer browse young hawthorn shoots before the thorns have
hardened, but can actually promote the successful growth of hawthorn plants by
browsing back many competitors more severely. Bees and other Hymenoptera, as
well as syrphid flies and numerous other Diptera, find the mass-flowering of
hawthorns a major seasonal source of pollen and/or nectar. The fruits of most
species are considered unpalatable in modern times, but those of a few species
are used in jams and jellies. Some species of hawthorns are cultivated as
ornamentals in Missouri, although there are relatively few disease-resistant
cultivars sold at nurseries in the state. The species that is the most popular
is C. phaenopyrum, but a few mainly thornless cultivars of C.
crus-galli and C. viridis also are grown, and additional species are
occasionally cultivated as specimen plants. The very hard wood is sometimes
used in handicrafts. A few species have medicinal value, principally in
treating hypertension (Kurz, 2003).
In 1923, the
“white hawthorn blossom” was designated as Missouri’s official state floral
emblem by the state legislature. This was not without controversy, as some
botanists complained that establishing a state flower based on such a
taxonomically cantankerous genus and without designation of a particular
species was inappropriate (Bush, 1927). However, intense lobbying, mainly by
the Daughters of the American Revolution, swayed the politicians. Because the
precise wording of the bill mentioned red haw, most of the few botanists and
other natural history enthusiasts who care about such details have interpreted C.
mollis to be the species involved, but this interpretation stands on shaky
legal ground.
In Missouri,
hawthorns are much less numerous in nature than they were 100 years ago,
probably due to several interacting factors, including urbanization, conversion
of land to crop fields, fire suppression, fencing of open range, and other
changes in land-management practices, as well as the increasing abundance of
eastern red cedar (see below) and possibly even increasing populations of
nonnative songbirds (which can serve as seed dispersal agents for junipers). In
general, hawthorns grow, flower, and become established less well under
increasing canopy density in woodlands. The decline in hawthorn abundance in
the state is reflected in the fact that the vast majority of the more than
4,000 herbarium specimens of Crataegus accessioned in various herbaria
were collected before 1940. However, in spite of the major ecological changes in
the state since colonization by settlers of European descent, the genus
continues to be moderately common in Missouri.
Hawthorns are
susceptible to cedar apple rust (caused by Gymnosporangium
juniperi-virginianae Schwein. and related species), a fungus with a complex
life cycle involving species of Juniperus L. (in Missouri, mainly J.
virginiana L., eastern red cedar) as the alternate host. Symptoms of
infection by cedar apple rust in hawthorns include deformation of branches and
leaves, the presence of powdery orange patches on the plant surfaces, a
reduction in the amount of flowering (correlated with malformation of
branchlets), and abnormal development of fruits (resulting in amorphously
shaped fruits with small, orange, columnar outgrowths on the surface and
usually aborted seeds). Although small hawthorns can become so weakened that
the infection proves fatal, a main effect of this fungal disease is the
reduction in seed production, which is detrimental to recruitment of new
individuals over time. It is worthy to note, that of the nearly 1,600 specimens
of Missouri Crataegus accessioned at the Missouri Botanical Garden
herbarium up to and including 1937, very few show evidence of infection by
rust, but many of the more recently collected specimens show signs of such
damage. For more information, see the treatment of Juniperus
(Cupressaceae) in Yatskievych (1999).
There is not
strong consensus on the species-level taxonomy in Crataegus. Missouri is
especially problematic in this regard, because some of the premier collectors
of hawthorn specimens in the country during the period of 1880 to 1930 resided
in the state, notably B. F. Bush, John Davis, Henry Eggert, John H. Kellogg,
Kenneth Mackenzie, and Ernest J. Palmer (see biographical notes on these botanists
in Yatskievych [1999]). The specimens collected by these botanists fueled the
studies of hawthorn specialists of the era, notably Charles S. Sargent (1908,
1912), who eventually named about 130 species based on type specimens from
Missouri (Phipps et al., 2007). Palmer (1963) regarded some of these as hybrids
and reduced many of the older species to varietal status or synonymy, and
accepted 50 species in the state’s hawthorn flora. At the opposite extreme,
treatments such as those of E. L. Little (1979) or Gleason and Cronquist (1991)
include only about a dozen species for the state. Many of the taxonomic
ambiguities in species recognition have been attributed to the high incidence
of hybridization, polyploidy, and apomixis in the genus. However, in studying
specimens mainly from Missouri, Phipps (2005) concluded that putative hybrids
are restricted to relatively few, very local, sometimes apparently now extinct
entities. Instead, Phipps attributed much of the morphological variation to the
rather vigorous formation of local races within mainly the series Crus-galli,
Punctatae, Pruinosae, and Virides. On the other hand, in a survey of
rangewide cellular DNA content in hawthorns (using flow cytometry), Talent and
Dickinson (2005) found that tetraploids far outnumbered diploids, with triploid
taxa a relatively small, third group of taxa. Talent and Dickinson further
noted that diploids are self-sterile (requiring cross-pollination), whereas
most tetraploids are self-fertile and some are apomictic. Thus polyploidy and
apomixis have a role in the maintenance of local races and the fixation of
minor morphological differences within the reduced gene pools of such
potentially inbreeding or asexually (apomictically) reproducing plants.
A number of
putative hybrids are suspected among the Missouri Crataegus taxa treated
in the earlier literature. They were mostly discovered in the Ozarks during the
great period of exploration for Missouri Crataegus, roughly 1890–1935,
and most were described with binomials as good species rather than as
interspecific hybrids. Hawthorns were more abundant then and therefore the
opportunities for interserial hybridization were greater. It is notable that
relatively few of these persist to this date. The following is an alphabetical
list of these putative hybrids, with notes on their presumptive parentage and
abundance historically and presently in the Missouri flora. Crataegus sicca,
whose hybrid status is not fully understood, but which is extant at scattered
sites in the Ozarks and has been divided into two varieties by some authors, is
treated as a species in ser. Rotundifoliae and merely mentioned in the
list below. Crataegus rupicola, which may prove to be of hybrid origin
in the future, is discussed briefly under C. calpodendron.
C. ×atrorubens
Ashe (ser. Molles × ser. Virides). Described from the St. Louis area, last
collected in 1897, and apparently extinct in the wild; however still extant in
cultivation as specimen trees at a number of botanical gardens.
C. coccinioides
Ashe × C. mollis (Torr. & A. Gray) Scheele (ser. Dilatatae × ser. Molles).
Known from a few historical collections from Jefferson, Ripley, and Shannon
Counties; it was last collected in 1910.
C. collina
Chapm. × C. margarettae Ashe (ser. Punctatae × ser. Rotundifoliae). Known from
a few historical collections from Lincoln and Marion Counties; it has not been
collected since 1911.
C. collina
Chapm. × C. padifolia Sarg. (ser. Intricatae × ser. Punctatae). Known from a
single historical specimen collected in 1924 in Benton County.
C. ×danielsii
E.J. Palmer (ser. Crus-galli × ser. Virides [possibly C. engelmannii]). Rickett
(1937) regarded this as being quite common near Columbia (Boone County), but it
has not been collected since 1952.
C. ×dispessa
Ashe (C. treleasei Sarg., C. pyriformis Britton) (ser. Molles × ser. Punctatae)
(Pl. 528 f). Scattered historically in southern Missouri north locally to Boone
County; it was last collected in 1964 in Dallas County.
C. ×incaedua
Sarg. (C. pudens Sarg.) (ser. Crus-galli × ser. Punctatae [C. collina]).
Scattered historically in southern Missouri; it was last-collected in 1987 in
Camden County.
C. ×kelloggii
Sarg. (ser. Molles × ser. Rotundifoliae [C. margarettae]). Originally collected
in Marion County and the city of St. Louis; it was last collected in Greene
County in 1926. This striking taxon produces yellow fruits.
C. ×latebrosa
Sarg. (C. noelensis Sarg.) (ser. Molles × ser. Punctatae) (Pl. 528 h).
Collected historically more than 50 times in the southern half of the state; it
was last-collected in 1953 in Dade County.
C. ×lawrencensis
Sarg. (probably ser. Crus-galli × ser. Virides). Not seen since the few
original collections in 1903 and 1908, all from Jasper County.
C. neobushii
Sarg. × C. pruinosa (H.L. Wendl.) K. Koch (ser. Intricatae × ser. Pruinosae).
Known from a single historical specimen collected in 1907 in Taney County.
C. ×nuda Sarg.
(ser. Crus-galli × ser. Macracanthae [perhaps C. succulenta]). Described from a
collection made in Taney County; it was last-collected in 1952 in Lawrence
County.
C. ×permixta
E.J. Palmer (C. intermixta Sarg., an illegitimate name) (ser. Crus-galli × ser.
Virides) (Pl. 525 p). Described from the Hannibal area (Marion, Pike Counties),
it has not been collected since 1913.
C. ×persimilis
Sarg. (C. swanensis Sarg.) (ser. Crus-galli × ser. Macracanthae). 2n=68. Known
from a few historical collections from Taney County (the original material upon
which C. swanensis was described), but also a Dent County specimen collected in
2004 by Alan Brant.
C. sicca Sarg.
(possibly ser. Pruinosae × ser. Rotundifoliae). See the treatment in ser.
Rotundifoliae.
C. ×simulata
Sarg.(ser. Crus-galli × ser. Macracanthae [possibly C. macracantha]) (Pl. 526
c). Known from a number of historical collections from Jasper and Lawrence
Counties; it was last-collected in 1956 in Lawrence County.
C. ×vailiae
Britton (ser. Macracanthae [probably C. calpodendron] × ser. Parvifoliae [C.
uniflora]). Known from a number of historical collections in the southern half
of the state and still extant at several sites; it was last collected in 1997
in Howell County. See the treatments of C. uniflora and ser. Macracanthae for
further discussion.
C. ×verruculosa
Sarg. (ser. Crus-galli × ser. Punctatae [probably C. collina]) (Pl. 530 i–k).
Scattered historically in the southern half of the state and apparently still
extant at a few sites; it was last-collected in 2002 in Iron County.
The series Crus-galli,
Punctatae, Pruinosae, and Virides mainly appear recalcitrant to any
straightforward taxonomy, and the account given here gives priority to the
ability to unequivocally recognize taxa. The descriptions provided below for
those Missouri series with more than one species apply only to Missouri taxa
and mostly also exclude putative interserial hybrids. In using the keys, the
leaf shapes referred to are those near the center of variation on the flowering
branches, except where extension shoots are specifically indicated. The values
given for leaf lobing are characteristic for the deepest lobes on a leaf.
Because most hawthorns are considered difficult to identify, botanists should
give priority to collecting fresh flowering material or ripe fruiting material
with accurate color notes on the anthers or fruits (these can change color upon
dessication). When fruits are present, it is also helpful to remove stones
(nutlets) from a few representatives, as this is easier to accomplish while the
pomes are fresh rather than waiting until they are dried. Serious students of
the genus generally attempt to collect matching flowering and fruiting
specimens from marked individuals. However, material with spent flowers and
immature fruits usually can be determined to species.
As has been
traditional, the Missouri species of Crataegus are here classified into
series. A key to the determination of series follows.