EXOTIC SPECIES OF CELTIS (CANNABACEAE) IN THE FLORA OF NORTH AMERICA

2008·9.1 MB·English

by  Alan T Whittemore

(CANNABACEAE)
OF
EXOTIC
SPECIES CELTIS
NORTH
AMERICA
THE FLORA OF
IN
AlanT.Whittemore
US Arboretum
National
New
NE
3501 Ave
York
DC
USA.
20002-1958
Washington,
ABSTRACT
The genus (Cannabaceae, Ulmaceae; Sytsma 2002) a widespread group of ca. 60
traditional et is
Celtis L. al.
and growing north temperate zone. Several species are
or 70 species of trees shrubs, about half in the Celtis
North America. Most commonly cultivated are two native species, Celtis occidentalis L. (hack-
cultivated in
Two Mediterranean
berry) and laevigata Willd. (sugarberry). exotic species, C. australis L. (native to the
C.
and
basin and southwest Asia; Browicz and Zielinski 1982; Tutin 1991; Zielinski 1979) C. sinensis Pers.
(native to China and Japan; Fu et 2004), are available in the nursery trade. Both are planted, primarily
al.
warm
occasionally
mainly in interior valleys of California (Brenzel 2001). Celtis sinensis is
as street trees,
and sometimes considered species
planted in the eastern United States (Meyer et 1994; Dirr 1998), is a
al.
with potential for more widespread use as a landscape tree (Dirr 1998).
known weedy and urban The
Native species are well to be in gardens disturbed areas. single
Celtis
report of C. australis escaping in Butte Co., California by Oswald (1994) is the only report of a non-native
No
any
reproducing outside of cultivation in North America. exotic species of Celtis is treated in
Celtis sp.
and
Wilken However,
North America (Barker 1997; 1993). Batianoff Butler
continental or regional flora for
where
Queensland,
(2002) considered one of the worst invasive plants in south-east Australia,
sinensis
Celtis
they found capable of crowding out native vegetation and forming monocultures, suggesting that the spe-
it
become
has the invasive in suitable conditions.
potential
cies to
were
Herbarium specimens and were examined. Several field sites in California
field sites for Celtis
confirmed and The was also found to escape in a single location in the District
for C. australis C. sinensis. latter
Columbia.
of
and
Nesom
uniform terminology describing the "reproductive status
(2000) suggests simple, for
a
Uniform necessary allow
non-native treatment of invasives certainly to
dispersive success" of species. is
Nesom
meaningful comparisons between works. However, the simple categories suggests are often
different
apply newly escaping woody plants or other perennials with long generation times. Distin-
difficult to to
on
between Nesom's "waif1 and "naturalized" depends the scientists' estimate of the
guishing categories of
annuals perenni-
long-term reproductive behavior of the species in the habitat. This often suitable for or
is
may many
when woody where be
that are short-lived or reproduce young, but not suitable for plants, it
als
population and reproduce in the habitat can be estimated
years before the long-term ability of a to persist
known
accurately— can be whether the population naturalized. Unfortunately, the early
before
thus, is
it
Journal of the Botanical Research Institute of Texas 2(1)
IS
when
most
>tablishment phase precisely the period information about invasive tendencies of the species
is
is
eeded. becomes important document the habitats these species colonize and record their dispersal
to
It
istances from seed sources. Invasive species have often gone unrecognized for long periods because they
&
(Luken Whittemore
not included in regional herbaria, floras, or other literature Thieret 1995; 2004).
:e
&
McMinn
American Maino
hese two species are not described or illustrated in any North flora (except
A
who
and provided
247, included C. australis as a cultivated species). key, descriptions illustrations are
dow
ensure populations can be recognized by
that their local botanists.
to
Identification of in North America greatly complicated by unresolved taxonomic problems in a
Celtis is
variable complex of shrubs and small distributed over most of the United States, that are probably
trees,
apomictic (Whittemore 2005a). These plants (referred to as the "small tree complex" below) are treated in
names commonly
different floras under a variety of (the most used, in the order they were first published, are
and
Engelm. ex Koch,
Celtis pumila Pursh, C. tenuifolia Nutt., C. reticulata Torr., C. lindheimeri K. C. georgiana
None Furthermore,
Small). of the published treatments presents the variation in these plants adequately. of
the names above, only pumila and have been typified, and the correct application
five listed C. C. reticulata
names complex
an adequate taxonomic treatment
of the other in question. Until of this available,
is is
is it
not possible write key the North American species of Furthermore, shows a very high
to a full to Celtis. Celtis
level of within-plant leaf polymorphism, which greatly complicates identification. Leaves of juvenile or highly
same and
stressed plants are often very different from leaves of normal adults with the genotype, leaves of
may much may
vigorous leaders be larger than leaves of fruiting laterals, and these two leaf types differ very
strongly in shape, especially in and species of the small tree complex. Reliable identification of
C. occidentalis
may
spp. require studying material, and comparing leaves that are subtending pedicels (Fernald
Celtis fertile
1950, Whittemore 2005b). The key below includes species that grow outside of cultivation in the
all Celtis
United States and Canada, but does not attempt to divide the small tree complex into natural taxa. For the
taxonomy and Dahlberg
of subg. Mertensia (Kunth) Planch., see Berg (2001).
Celtis
many
Stems with prominent nodal Flowers dense cymes, hermaphroditic flowers with male flow-
spines.
in
.
cyme
lower on the same (branch on each lobe again deeply
ers scars visible pedicel). Styles bisbifid
(i.e. is
Mertensia
divided) Celtis subg.
x
Nodal spines straight. Leaves 1-3(-5) 0.4-2 cm. Axils of basal veins with deeply invaginated domatia.
2.
m
New
2-6 ehrenbergiana
Shrubs Texas, Mexico, Arizona Celtis
Florida,
tall.
Liebm.
(Klotzsch) (=Celtis pallida
Torr.)
x cm x cm
Nodal spines curved. Leaves 5.5-1 2.5-4 3 6 the tropics). Axils of basal veins without
2. (to in
1
m
5-12 iguanea
domatia. Shrubs (often scandent) Florida Celtis (Jacq.) Sarg.
tall.
Stems unarmed. Hermaphroditic flowers solitary on axillary pedicels (without branch scars on pedicel). Styles
I .
ed lobes) Celtis subg. Celtis
Abaxial surface of uniformly pubescent over abruptly con-
leaf ?af
3.
tracted to slender acumen, each margin with 20-32 teeth Celtis australis
a
acumen and no more
or the leaf blade evenly tapered or gradually narrowed to the slender entire or with
m
and
Large shrubs or small trees to 2 with leaning trunks horizontal or arching leaders or (with
4.
tall,
1
0%
seldom more
age) multiple spreading trunks. Pollen largely or entirely aborted, than of the grains
1
number
and
stainable with acetocarmine, stainable grains present) very variable size of pores, or
in
(if
complex"
else anthers remaining small and indehiscent. "Small tree
m
one
Excurrent trees to 30 typically with strong vertical trunk (occasionally 2 or 3 parallel upright
4.
tall,
95-100%
with acetocarmine.
3-porate, stainable
extending (0.5-)0.6-075 length of blade; bark without corky outgrowths Celtis sinensis
acuminate
Leaves subtending pedicels lanceolate, obliquely triangular or triangular-ovate, (usually
5.
slenderly basal secondary veins extending 0.3-0.55 length of blade; bark with prominent corky
so),
629
Whittemore, Exotic species of Celtis in the North American flora
Leaves generally bright green on both surfaces; leaves subtending pedicels evenly tapering or
6.
gradually narrowed to the slender acumen; leaves of vigorous leaders larger but similar shape;
in
mm
6-8
mature drupes brownish-orange laevigata
diameter, or red Celtis Willd.
in
Leaves generally paler abaxially; leaves subtending pedicels abruptly narrowed to the acumen;
6.
leaves of vigorous leaders larger and different shape (often lanceolate or oblong, apex acute
in
mm
or short-acuminate, base often shallowly cordate); mature drupes 8-1 diameter, dark
in
1
may
brownish purple or purplish red (but immature drupes be red or orange) Celtis occidentalis L
brown
roughened. Branchlets or purplish,
:ly
mm mm
brown 3-5
pubescent with spreading hairs 0.5 long. Winter buds or purplish, long, puberulent.
to
mm,
3-6 9-17
Stipules linear or lanceolate, pubescent, fugacious. Leaves subtending pedicels with petiole
mm,
tan, pubescent, dorsal sulcus usually a narrow sharp groove, seldom broad and shallow; leaf blade
3-5
8-11
narrowly elliptical to lanceolate or lance-ovate, x cm, rather thick but flexible, adaxial surface dull
dark green, abaxial surface green or glaucous, pubescent with spreading hairs over veins and whole
light
2-4
blade, the touch; secondary veins on each basal secondary veins extending
felty to side, (0.45-J0.5-0.7
margin from apex
length of blade; base cuneate to rounded, usually strongly asymmetrical, serrate base to
mm
with sharp teeth 2-3 long, teeth 20-32 on each side; leaf apex abruptly contracted to a slender acumen;
cm
Male
leaves of sterile leaders similar but often larger, to 16 long. flowers fascicled in axils of bud-scales
and emerge
lower leaves, bisexual flowers solitary in lower leaf axils, reaching anthesis as leaves in the
mm
Drupes pubescent 19-31
spring. Pollen not seen. 1 per leaf axil, pedicel (at least proximally), long,
Drupe
1.6-2.7 times as long as subtending petiole. subglobose to pyriform, usually tapering to style-base,
mm
10-12 brown
very dark
in diameter, (almost black) maturity.
at
—
15-60
Distribution and Flowering. Found in North America in riparian woodland, m. Flowering
elev.
emerge mid-
as leaves in the spring; fruiting to late
fall.
can be recognized by smooth or roughened bark (not developing corky warts or
finely
Celtis australis its
ridges like the native North American species), leaf blades that are sharply serrate and very slenderly
its
body and
long-acuminate from narrowly lanceolate or lance-ovate uniformly felty-pubescent
a elliptical to
beneath, and dark brown or black drupes (the drupes ripen orange-brown, red or purplish in
large,
its
American
other
species).
Oswald
was reported by (1994) as an escape in Bidwell Park, Chico, California. This
Celtis australis site
was visited in August 2006. The road between the of the former Forestry Station and the current Nature
site
many now
and
Center lined with well-established evidently planted years ago fruiting heav-
large, trees,
is
common
and The found
Seedlings saplings are in the vicinity of these majority are in disturbed
trees.
ily.
open woodland
roadside habitats, but well-established small trees are also found in Quercus lobata Platanus
-
Some
in the vicinity of the planted trees. of these trees are fruiting in this habitat, so C. australis is definitely
established in native habitats and should be considered locally naturalized.
Feral plants of Celtis australis were also found along a waterway on the north side of Davis, in dense
when
secondary grew up on exposed waterway was channelized approximately
disturbed the
forest that soil
No much
emp-
thirty years ago. cultivated trees were seen nearby, but the storm-drain system from of Davis
ties into this waterway, so seeds could easily have washed in from elsewhere in Davis (where C. australis is
The under under
occasionally planted as a street land not cultivation, so a strict application of the
tree). is
Nesom
on
definitions of (2000) these trees are either waifs or naturalized (depending their ultimate ability to
was and
reproduce themselves but the heavily disturbed during the channelization, receives
locally), site
it
Journal of the Botanical Research Institute of Texas 2(1)
C
Fig. 1 Foliage and drupes of introduced Ceitis species. A. C. austratis. B. sinensis.
.
The worth how<
noting,
site is
Ceitis sinensis Pers., Syn. 1:292. 1805. (Fig. lb).
Pi.
m
Deciduous 20 Bark smooth roughened. Branchlets brown, brown-pubescent,
or finely
trees to gray,
tall.
mm
sometimes becoming Winter buds dark brown, 1-3 long, glabrous or puberu-
glabrescent in season.
late
mm,
3-5 pubescent, fugacious. Leaves subtending pedicels with petiole
Stipules linear or lanceolate,
lent.
mm, 3-10
3-10 brown, pubescent, dorsal sulcus broad and shallow; leaf blade ovate to ovate-elliptic, x
3.5-6 cm, rather thick but adaxial surface glossy dark green, abaxial surface light green, usually
flexible,
when on
yellowish-brown puberulent young, maturity with hairs abaxially scattered
inconspicuously
at
3-4
on
major veins and sometimes tufted in vein smooth to touch, secondary veins each side, basal
axils,
secondary veins extending (0.5-)0.6-0.75 length of blade; base rounded, obtuse, or obliquely truncate,
0-16 on
on each
subsymmetrical moderately oblique, margin subentire to crenate apical half, teeth side,
to
cm
Male
apex acute or short-acuminate; leaves of sterile leaders similar but often larger, to 9 long. flowers
and lower reaching an-
fascicled in axils of bud-scales lower leaves, bisexual flowers solitary in leaf axils,
uniform uniformly
thesis as leaves emerge in the spring. Anthers dehiscent, pollen grains in size, 3-porate,
pubescent
97-990/0 stainabl with acetocarmine. Drupes l(-3) per leaf axil, pedicel rather stout, (at least
e
mm
mm
Drupe
proximally), 4-10 long, 1-1.5 times as long as subtending petiole. subglobose, 5-7(-8) in
brownish orange
diameter, maturity.
at
.
Whittemore, Exotic species of Celtis in the North American flora
km N Orange
sand and 120 m, 436 (CHSC).
willows, 0.5 of Pentz Mesilla Valley Rds., elev. ca. B. Castro
ca. jet.
UCIr
"r
^^^^^^^5^^.
o Spontaneous
Co.:
5
"id
I13d
H
iE
Crt! !
g
>loCc Spontaneous
'~rEBs^B5i=:B£
.: tree
can be recognized by smooth bark, rather leathery, glossy leaves, with the margins usu-
Celtis sinensis its its
and apex
ally crenate or bluntly serrate the often rounded-acute.
Celtis sinensis has never been reported to escape in North America, but field sites and herbarium
and
specimens were found documenting populations over a surprisingly wide geographic range in a
feral
common
any and no evidence can be an
variety of habitats. not at of the sites there is currently that
It is it
and
but
aggressive competitor in our reported for Australia; Batianoff Butler 2002), saplings are
flora (as
often found several hundred meters from possible seed sources, suggesting that effective dispersal agents
On
Arboretum Washington DC,
for this species exist in North America. the grounds of the U. S. National in
m
100-300
from
young trees are occasionally found in open margins of native deciduous forest, often the
weed
nearest possible seed source, but plants have not been observed in closed forest (except as a in
feral
cultivated beds). The Butte County (Castro 436) riparian woodland in dry, grassy low foothills of the
site is
m
and herbarium 200 from planted
northern Nevada, according the the plants are
Sierra to label, feral ca.
A
trees of C. The tree near Road 101 in Yolo County (Whittemore 06-012) is in native alkali grassland
sinensis.
some
has never been but has probably been subject disturbance because of proxim-
that cultivated to its
m
The
and 300 from seed
county road This the nearest possible source.
ity to the railroad. tree is at least
long dispersal distances seen most of the are not surprising, since the sweet, fleshy drupes are well
at sites
shown
suited bird dispersal. Fleshy bird-dispersed fruit has been to be a significant predictor of invasive
to
woody
behavior in plants (Widrlechner et 2004), so further tracking of this species is desirable.
al.
War
would thank Lawrence Janeway and
like
to
I
Andrew comments on
Sanders providing hat
for
comments on
manuscript.
Ertter for helpful the
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Menlo
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K.N. Ed.
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1