Plant Species Biology (2008) 23, 152–158
doi: 10.1111/j.1442-1984.2008.00224.x
Breeding biologies, seed production and species-rich bee
guilds of Cleome lutea and Cleome serrulata
(Cleomaceae)
JAMES H. CANE
US Department of Agriculture–Agricultural Research Service, Bee Biology and Systematics Laboratory, Utah State University,
Logan 84322–5310, United States of America
Abstract
The summer-blooming annual forbs Cleome lutea and Cleome serrulata (Cleomaceae) are
native across the US Intermountain West and Rocky Mountains, respectively. Their
farmed seed is sought to help rehabilitate western rangelands in those regions. This study
of the reproductive biologies and pollinator faunas of C. lutea and C. serrulata is the first
for this cosmopolitan family, the sister family to the Brassicaceae. Unlike the S-allele
self-incompatibility systems of some Brassicaceae, both species of Cleome were found to
be self-fertile and capable of some autogamy. Compared with selfing, outcrossing did not
enhance seed set, seed viability or seedling vigor for either species (in fact, selfed progeny
were more robust). Large, openly visited plants yielded >20 000 seeds each. Like several
species of the sister family Capparaceae, flowers of both species first shed their pollen,
secreted nectar and became receptive nocturnally. Although no nocturnal visitors were
found, both Cleome species attracted a diverse array of diurnal native bees, wasps and
butterflies. Among the many floral generalist bees that work Cleome flowers for pollen
and nectar are two managed agricultural pollinators, Apis mellifera and Megachile rotundata. These observations bode well for pollinating C. lutea and C. serrulata in small
commercial seed fields. It appears that diverse wild bees would benefit from the addition
of native Cleome to restoration seed mixes, with the objective of sustaining native pollinator faunas during the first few years of postfire plant community rehabilitation.
Keywords: Apiformes, Brassicaceae, Capparaceae, pollination, seedling fitness, self-compatibility.
Received 3 January 2008; accepted 24 July 2008
Introduction
The small cosmopolitan eudicot family Cleomaceae (300
species) is the sister family to the more diverse Brassicaceae; it also shares characters with the Capparaceae
(= Capparidaceae), with which it has been formerly classified (Hall et al. 2002). Dominating the family Cleomaceae
are the 180–200 species of the type genus Cleome (called
‘spider-flowers’ or ‘bee-plants’) that occur in many
warmer regions of the world (Iltis 1957; Sanchez-Acebo
2005). Some are annual forbs common in disturbed habitats; others are woody, but short-lived. Knowledge of the
breeding biologies of Cleome species might be relevant to
Correspondence: James H. Cane
Email: jim.cane@ars.usda.gov
the evolution of self-incompatibility systems in the Brassicaceae, and is certainly needed to successfully farm
Cleome seed for large-scale rangeland restoration projects.
Native species of Cleome might have a unique role to
play in plant community restoration in xeric valleys and
plains of the US Intermountain West. Rehabilitating
western USA rangeland plant communities has long
included reseeding, but primarily with grasses and
shrubs. Seed of several native forbs are now being grown
commercially for this purpose, with more to follow (Cane
2008), but these are all herbaceous perennials that typically do not flower in the year after seeding. In contrast,
Cleome are annuals that can provide bloom quickly and, if
used by a diverse array of wild bees, might help sustain
pollinator communities the year after an autumn restoration seeding. Larger quantities of affordable seed from
Journal compilation © 2008 The Society for the Study of Species Biology
No claim to original US government works
P O L L I N AT I O N N E E D S O F CLEOME
native Cleome species, if available from seed farmers, could
be added to seed mixes that are used to rehabilitate vast
burned rangelands of the Great Basin and neighboring
biomes of western USA (Cane 2008).
Farming seed crops generally requires pollinator
supplementation to realize potential seed yields (Free
1993), but how much can depend on a plant species’
breeding biology. The Brassicaceae, sister group to the
Cleomaceae, has a distinctive sporophytic incompatibility
(SI) system (Charlesworth et al. 2005) and only pollen flow
between plants sets seed. However, species of Cleome are
early successional species at disturbed sites; such
attributes in other species are often associated with selffertility and autogamy (Baker & Stebbins 1965). Thus, ecological versus phylogenetic inferences give contrasting
predictions for the pollination needs of Cleome.
To evaluate the pollination needs of a plant, the breeding biology of the plant must be understood. The objectives of the present study were to characterize the floral
and breeding biologies of two of the six species in Cleome
section Peritoma (Iltis 1957), Cleome lutea (yellow or
Nevada bee-plant) and Cleome serrulata (Rocky Mountain
bee-plant). The necessity or benefit of pollinators and
cross-pollination was evaluated for producing fruits,
fertile seeds and vigorous progeny. Flowering phenology
and the timing of stigma receptivity and anther dehiscence were characterized. Data from museum specimens
and limited field collections of flower visitors to these
plants were also compiled to document pollinator species
richness and the attributes of the pollinator guilds.
Materials and methods
Traits of Cleome lutea and Cleome serrulata
Both species are robust, tap-rooted annuals native to the
xeric valleys and plains of western North America. They
are typically found at disturbed sites, such as waste
places, margins of washes or barren sandy desert plains
(Iltis 1957). Owing to its beauty, C. serrulata has been cultivated in gardens in and beyond its native range in
western USA. Plants of both species are erect (3–25 dm
tall), glabrous and malodorous. They invariably produce
one or more compact, bracteolate terminal racemes. Individual racemes are indeterminate, continually producing
new flowers for weeks during the summer. The round
seeds (2–4 mm in diameter) are borne in siliques. The
seeds lack an endosperm (Sanchez-Acebo 2005) and
require moist cold stratification for embryo development
and germination.
Flowering
Individual plants of both Cleome species produce two
types of like-sized showy flowers (yellow for C. lutea and
Plant Species Biology 23, 152–158
153
Fig. 1 Flower, fruits and seeds of Cleome lutea. Shown are the
pistil atop its gynophore and the dehiscing anthers of this hermaphroditic flower, an immature and mature fruit (silique), and
its dehiscent valves removed to reveal the loop-like replum and
the content of mature dark seeds. Inset: X-ray positive of C. lutea
seeds showing viable (X-ray dense) and non-viable (gray)
embryos.
magenta for C. serrulata). Hermaphroditic flowers have six
stamens and a large pistil atop a stalked gynophore
(Fig. 1). Staminate flowers have rudimentary pistils that
never set pods (Stout 1923). However, Cleome are not
andromonoecious. A staminate flower begins as a hermaphroditic bud; its pistil thereafter fails to develop fully.
When a raceme is shunting resources to many maturing
fruits, most of its flowers become staminate. Over the long
flowering season, racemes alternate between the production of staminate and hermaphroditic flowers (Murneek
1937); thus, maturing siliques and shedding seed while
continuing to bloom.
Daily blooming phenologies were observed on plants
grown in two common gardens in Logan, Utah, USA
(41°45′ N, 111°48′ W). To judge stigma receptivity, excised
pistils were individually inserted into a Pasteur pipette tip
filled with hydrogen peroxide (J. Thomson, pers. comm.,
1999). Receptivity was indicated by the visible generation
of oxygen bubbles on the bare stigma, the result of peroxidase activity (Zeisler 1938).
Breeding biology
Seeds were commercially collected and pooled from wild
populations in Utah. The seeds were shallowly planted
outdoors in autumn 2003 at the common garden of the Bee
Biology and Systematics Laboratory in Logan, Utah, USA.
The following summer, the clay loam soils were infrequently irrigated as needed to maintain plant vigor. For
each of the four pollination treatments, six well-separated
individuals per species of similar size, vigor and bud
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154 J . H . C A N E
development were chosen, randomly assigned their
treatment, and tagged. These plants were enclosed in
7 m ¥ 7 m ¥ 2 m walk-in field cages made of Lumite
screening (Synthetic Industries, Chicopee, GA, USA) to
exclude flower visitors. Individual pollinator exclusion
bags were not used because, in earlier trials, we found that
flowers on the crowded tall racemes of Cleome transfered
pollen by passively rubbing or jostling against the
bag netting. Once the flowers began to shed pollen, each
new flower on every tagged raceme was marked and
pollinated.
During June and July, two manual pollination treatments were applied to newly opened flowers of the caged
plants: geitonogamy (transfer of self pollen) and
xenogamy (outcrossing). As younger crowded plants
often produced single racemes, whose flowers proved difficult to tag individually, different plants received single
treatments. Geitonogamous pollination involved rubbing
the day’s recipient virgin stigmas with fresh anthers from
an untagged flower from the same plant. Donor anthers
for xenogamy were taken from untagged plants. Optical
magnifying visors were used as necessary to visually
confirm pollen transfer. Floral racemes were manually
pollinated daily until a plant shifted from producing hermaphroditic to staminate flowers. Six other plants per
species in the cages served as controls for autonomous
self-pollination (autogamy). Apomixis was impractical to
evaluate because the flowers would have needed to be
nightly emasculated when they first opened. Adjacent to
the pollination treatment cages, six additional tagged
plants per species were used as positive controls that were
freely visited by pollinators.
The pollination treatments were compared by species
using general linear model anova tests for percentage
fruit (silique) set (arcsine or log10 transformed) and for
their yields of dark seeds per silique. In general, only the
dark seeds possessed developed embryos. The data transformations yielded acceptable normality (Shapiro–Wilk
statistic, P > 0.01 or better) and homogeneous variances
(Levene’s test, P > 0.04 or better). When differences were
found among treatments (P ⱕ 0.05), the treatments were
compared by Ryan–Enot–Gabriel–Welch (REGW) a posteriori tests (Ray & Sall 1985).
Seed production
Once siliques were mature, but before they dehisced, they
were individually removed and returned to the laboratory. Siliques per raceme and the individual contents of
the dark seeds were counted (Fig. 1). To estimate and
compare seed viability, embryo development was compared for plump seeds differing in color (dark vs pale)
using X-ray imagery (HP 4380 N Faxitron; Hewlitt
Packard, Salt Lake City, UT, USA; 25 KV, 30 s exposure,
medium grain industrial film) (Fig. 1) from lots of 20
seeds per species and color, representing all pollination
treatments. Persistently pale seeds and pale seeds that had
darkened 1 week after harvest were X-rayed again and
their germination evaluated. Two lots of 10 dark seeds
each per species were weighed.
Three large, mature, intact plants of C. lutea were taken
at the end of flower production. The life-time silique production per uncaged plant was determined by counting
their complements of siliques and replums (a loop of
tissue that persists after the valves of the siliques have
dehisced) (Fig. 1). Lifetime seed production was then estimated by multiplying by the average numbers of seeds
per silique for that species.
Seedling vigor
Harvested seeds of C. lutea and C. serrulata from manually
selfed and outcrossed flowers were placed in cold (4°C)
storage for 4 months and then planted individually in
‘conetainers’ in a heated glasshouse. On 19 April 2005,
seedlings were measured for size (height, length and
width of largest leaflet). Once the data were transformed
(log10), the variances were homogeneous (Levene’s test)
and the data were normally distributed (Kolmogorov–
Smirnov test). The performance of plants from outcrossed
versus selfed seed was compared by general linear model
anova followed by REGW a posteriori tests where warranted (Ray & Sall 1985). Statistical significance in all cases
was P ⱕ 0.05.
Results
Flowering
The flowers of Cleome presented an unexpected phenology given the diverse diurnal pollinator fauna revealed by
this and other studies (e.g. Messinger 2006). All new
flowers of both species opened nocturnally, starting 1–3 h
after sunset. No new flowers were added during daylight
hours. For C. lutea, newly opened flowers from 10 plants
were checked 150 mins after sunset on 13 July
(23.30 hours mountain daylight savings time [MDST]).
New pistils (n = 15) of C. lutea flowers were large, and
each stigmatic tip was suffused with red pigment. Their
pollen-free stigmas all produced frequent bubbles when
immersed in hydrogen peroxide, indicative of their receptivity. The anthers of half of these flowers had begun to
dehisce, each anther first rupturing at its distal tip. For
C. serrulata, the petals had unfurled by approximately
90 mins after sunset on 7 August. One or more nectar
droplets was visible in 90% of these opening flowers,
although at this hour only 2 of 18 flowers had dehiscing
anthers and none showed stigmatic peroxidase activity.
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No claim to original US government works
Plant Species Biology 23, 152–158
P O L L I N AT I O N N E E D S O F CLEOME
During the hours after sunset, no flower visitors were
observed in the large uncaged plots of either species in the
northern Utah common gardens, although the nights
were warm and calm. By dawn, all new flowers of both
species had opened and possessed fully dehisced anthers,
receptive stigmas and large droplets of viscous nectar
(large enough in C. serrulata to rain out of shaken plants).
From an isolated C. lutea plant inspected just before
sunrise, 11 of 17 stigmas from new flowers lacked pollen,
and the remaining stigmas had <10 grains. Later that same
sunny morning (10.30 hours MDST) after several hours of
general bee activity, 14 of 15 stigmas bore pollen (most
had >15 grains) on fresh flowers of the same plant. Thus,
some stigmas of C. lutea receive pollen at night, apparently passively by autogamy; however, more thorough
pollination occurred during morning bee activity.
Breeding biology and seed production
Both C. lutea and C. serrulata are fully self-fertile. Autogamy yielded considerable numbers of siliques and seeds
for both species (Table 1). Autogamy is facilitated by the
stamens coiling inward later in the day. For C. lutea,
equivalent proportions of flowers set fruits in the autogamy, geitonogamy and xenogamy treatments; flowers
accessible to pollinators were two–threefold more fruitful
(Table 1). The average counts of fertile seeds per silique
did not differ between treatments. In C. serrulata, autogamy was inferior to the other treatments, with autogamous flowers setting fewer siliques (F3,18 = 3.39, P < 0.04)
each with fewer seeds (F3,228 = 20.49, P < 0.0001) (Table 1).
Neither xenogamy nor pollinator access improved on geitonogamy for either fruit set or seeds per silique. Comparing the two species, siliques of C. serrulata produced
threefold more mature seeds than those of C. lutea in all
but the autogamy treatment (Table 1).
155
The X-ray images of seeds from both Cleome species
revealed the folded embryo within. Images of seeds could
be visually classed into two groups, those possessing an
X-ray dense embryo (dark in positive image) (Fig. 1 inset)
and those whose embryo was less dense (gray). Dark
seeds invariably had an X-ray dense embryo and were all
readily germinable, whether dark at harvest (20 of 20
images) or darkening in the week after harvest (20 of 20).
Pale seeds at harvest sometimes lacked the visually distinct embryo (5 of 20); those that remained pale 1 week
after harvest mostly lacked developed embryos (14 of 20).
Mature dark seeds of both species were comparable in
weight, averaging 6.7 mg each (for an estimated 150 000
seeds per kg).
In the common garden, three large openly visited
C. lutea plants produced an average of 1470 siliques each
containing on average eight seeds, those of C. serrulata
produced 1229 siliques with 21 seeds each. In a dense
vegetated part of the plot, 22 C. lutea plants grew in 0.1 m2,
yet even these averaged 6.6 ⫾ 3.6 racemes per plant. One
big C. lutea raceme set large seeds from 80% of its 336
flowers. The C. lutea plants averaged 110 ⫾ 61 racemes per
m2 of plot.
Seedling vigor
Progeny of C. lutea grown in the glasshouse from seed
that was dark at harvest (‘early’) were similar in size to
those from seed that darkened the week after harvest
(‘late’). Seedling progeny from these two seed maturation
classes (early or late) were equivalent in leaf and plant
dimensions (6–10 seedlings measured per species; P > 0.1
to P > 0.8). If the seed was viable (dark), then whether it
matured on or off the plant did not affect subsequent
seedling vigor.
Progeny from the two manual pollination treatments
were not equivalent in vigor in either species. Seedlings
Table 1 Comparison of fruit set, mature dark seeds per silique and progeny vigor for four pollination treatments of Cleome lutea and
Cleome serrulata
Reproductive
response
Cleome
species
Flowers setting fruit (%)
lutea
serrulata
lutea
serrulata
lutea
serrulata
lutea
serrulata
Seeds per fruit
Seedling height (cm)
Seedling longest leaf (cm)
Pollination treatment (⫾ SD)†
AutoGeitonXenogamy
ogamy
gamy
23 ⫾ 15
34 ⫾ 15*
6⫾4
8 ⫾ 6*
–
–
–
–
31 ⫾ 15
56 ⫾ 14
7⫾4
19 ⫾ 10
17 ⫾ 3.6*
13 ⫾ 3.7*
35 ⫾ 5.6*
25 ⫾ 3.0
26 ⫾ 16
63 ⫾ 22
7⫾4
22 ⫾ 11
11 ⫾ 3.6
10 ⫾ 2.4
25 ⫾ 3.4
26 ⫾ 3.0
Sum of measured
Freely
visited
Plants
Flowers
or fruits
76 ⫾ 13*
64 ⫾ 32
8⫾4
21 ⫾ 11
–
–
–
–
47
22
47
22
70
48
70
48
1235
720
263
232
–
–
–
–
†All statistical comparisons are between treatments within species. *Values are statistically different from other treatments within their
row (P ⱕ 0.05). Only seeds from manual pollinations were sown and compared for progeny vigor. SD, standard deviation.
Plant Species Biology 23, 152–158
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156 J . H . C A N E
resulting from geitonogamy were equal to, or larger than,
those from xenogamy (Table 1). For C. lutea seedlings of
like age, those from geitonogamy exceeded those from
xenogamy in both height (F1,69 = 43.3, P < 0.001) and
length of the longest leaf (F1,69 = 72.7, P < 0.001) (Table 1).
For C. serrulata seedlings of like age, those from geitonogamy were 25% taller than outcrossed progeny
(F1,47 = 6.7, P < 0.015), but seedlings from both treatments
were equivalent in leaf length and leaflet width (Table 1).
No xenogamy advantage was evident in these measures of
seedling performance.
Discussion
Both Cleome species possess pollination traits that have
long been considered favorable for colonists (Baker &
Stebbins 1965). Self-fertility enables the first individual
that colonizes a site to produce viable seed. The coiling
stamens of older flowers facilitate autogamy. Furthermore, progeny from geitonogamous seed grew at least as
vigorously as progeny from xenogamy. If pollinators are
absent, perhaps following some ecological perturbation
such as fire or flood, both Cleome species are capable of
autogamy and facilitated self-pollination. Selection is
expected to favor self-fertility of colonizing annuals like
Cleome when pollinator services might be unreliable (e.g.
soon after habitat perturbation) (Lloyd 1992). The rate of
expansion and persistence of Cleome populations in nature
is not known, but in our common gardens, the parent
plants set massive numbers of readily germinable seeds
that produced dense stands of seedlings the following
year. If representative of wild populations, even when
bees are present, these Cleome species are likely to be
under serviced by their pollinators in some years of
massive bloom, circumstances again favoring self-fertility
and a degree of autogamy.
Phylogenetic inference from sister families was not predictive of Cleome breeding biologies. These Cleome species
did not share the distinct SI system found in their sister
family, the Brassicaceae (Charlesworth et al. 2005). Meager
evidence from the Capparaceae (sister group to Brassicaceae and Cleomaceae) was not illuminating either, for
while Capparis flexuosa is self-fertile, C. verrucosa is reportedly self-incompatible (Zapata & Arroyo 1978).
The nocturnal anthesis of these Cleome flowers is puzzling. Most species of Brassicaceae flower diurnally. A
desert exception, Lyrocarpa coulteri, has drab, somewhat
tubular flowers that release a heavy Gardenia-like scent
after nightfall (J. Cane, pers. obs., 1994), attributes consistent with moth pollination. In contrast, flowers of both
C. lutea and C. serrulata are vividly colored and scentless
(to humans), attributes atypical for nocturnally pollinated
flowers (Faegri & van der Pijl 1979). The flowers attracted
no nocturnal visitors in the common gardens, but plenti-
ful bees, wasps and butterflies during daylight hours,
attributes shared with some other desert Cleomaceae (e.g.
Wislizenia, Cleomella and Oxystylis). With reference to the
Capparaceae, the flowers of Capparis ovata and Capparis
spinosa are nocturnal, the former pollinated by sphingid
moths, while those of C. spinosa (in Israel) are first visited
nocturnally by pollen-foraging Proxylocopa bees, but later
the next day by honey bees and other bees as well (Dafni
et al. 1987). Perhaps nocturnal anthesis is a persistent
ancestral attribute in these Cleome species. For now, no
satisfying ecological or phylogenetic explanation is apparent for the peculiar flowering schedules of these two
species of Cleome.
Beginning in the morning, diverse polylectic (i.e. generalist) bees, butterflies and wasps opportunistically
sought nectar and sometimes pollen from flowers of both
Cleome species in the common gardens (Fig. 2). Bees have
been extensively collected from wild C. lutea in southern
Utah, both for this study and from 4 years of exhaustive
bee surveys in Grand Staircase-Escalante National Monument (O. Messinger and T. Griswold, pers. comm., 2007).
Polylectic bees were found to be prevalent and widespread on C. lutea, accounting for 3/5 of the collected
specimens. Nearly half of the polylectic individuals
sampled belonged to just three genera of small-bodied
bees: Halictus, Hylaeus and Lasioglossum sensu lato, plus
diverse Perdita that are likely to be specialists on other
floral hosts. Bees less frequently collected from C. lutea
represent 28 other native bee genera: Agapostemon,
Andrena, Anthidiellum, Anthidium, Anthophora (Fig. 2),
Ashmeadiella, Bombus, Ceratina, Colletes, Diadasia,
Dianthidium, Dieunomia, Dufourea, Eucera, Exomalopsis,
Habropoda, Heriades, Macrotera, Megachile, Melecta,
Melissodes, Nomada, Osmia, Protandrena, Sphecodes, Stelis,
Triepeolus and Xylocopa. Overall, 140 species of native
bees have been taken from C. lutea in southern Utah,
Fig. 2 Digger bee (Anthophora californica) hovering to collect
pollen from the exserted anthers of a Cleome lutea flower.
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Plant Species Biology 23, 152–158
P O L L I N AT I O N N E E D S O F CLEOME
collectively representing many of the native bee genera
found in the western USA.
The fauna at C. serrulata has not been so exhaustively
sampled. Nonetheless, 62 species of native bees were collected in the Grand Staircase-Escalante National Monument survey, with 95% of those individuals representing
51 bee species shared with C. lutea (Messinger 2006).
Together, the 162 native bee species found on these two
Cleome species are a substantial fraction of the speciesrich bee community that inhabits the 730 000 hectares of
the National Monument (Messinger 2006). In particular,
one-third of the Monument’s entire fauna of polylectic
bee species (58% of all 656 species) were collected visiting C. lutea and/or C. serrulata. These two floral hosts
can be expected to attract and feed many additional
polylectic bee species throughout their broad geographic
ranges in the western USA (23 additional bee species in
the general collections at the Bee Biology and Systematics Laboratory were collected from C. lutea and C. serrulata). Flowering patches of Cleome attract and feed
diverse floral generalists from local bee communities,
underscoring the potential value of these plants for
native bee communities where summer floras are otherwise lacking bloom.
Other species-rich floral guilds of bees often include
numerous oligolectic species (taxonomic pollen specialists) because their hosts (e.g. Helianthus, Larrea, Salix,
Phacelia) present a ‘predictable plethora’ that oligolectic
populations can depend on for ample pollen (Wcislo &
Cane 1996). In contrast, the two Cleome species examined
in the present study appear to be opportunistic colonists
whose annual bloom varies greatly with patchy annual
rainfall. Only a single putative oligolege is associated with
either Cleome species, the tiny bee Perdita zebrata. Perdita
zebrata is common on C. lutea, accounting for half of the
2463 bees sampled from C. lutea in southern Utah. In turn,
the Cleomaceae account for 90% of all 1100 host labels for
this bee in the extensive US Department of Agriculture–
Agricultural Research Service bee collections at Logan,
suggestive of it being a Cleome specialist. Many of the
P. zebrata specimens caught from C. lutea were males, suggesting that they use Cleome flowers as likely sites to find
mates, a habit common among oligoleges (Eickwort &
Ginsberg 1980). A local bee community study found that
P. zebrata dominated C. lutea, rarely if ever visiting the
other abundant flowering species used by diverse native
floral generalists (Tepedino et al. 2008). Other than P. zebrata, the bee faunas found associated with C. lutea and
C. serrulata all appear to be floral generalists. This accords
well with the relative dearth of floral specialists associated
with members of the Brassicaceae (Hurd 1979; Gomez &
Zamora 1999), likely reflecting the fact that their populations are transient and their floral morphologies and
rewards are unspecialized (Wcislo & Cane 1996).
Plant Species Biology 23, 152–158
157
Farmed C. lutea and C. serrulata should produce prodigious quantities of seed. Multiplying together seeds per
silique (Table 1), siliques per raceme and racemes per
plant, each mature, well-pollinated C. lutea plant in the
common garden produced an estimated 11 000 viable
seeds (73 g fresh weight). Likewise, large plants of C.
serrulata each produced an estimated 26 000 seeds
(173 g). Conservatively, a farmed hectare of these two
Cleome species could produce nearly 2000 kg/ha of seed,
although the species’ indeterminate growth and flowering
would prevent harvest of all of that seed at once.
Adequately abundant pollinators will be necessary to
realize such prodigious seed production by these two
Cleome species; plants accessible to pollinators yielded
three–fivefold more viable seed than those limited to
autogamy (Table 1). Fortunately, these Cleome species are
broadly attractive to a diverse array of generalist bees,
including commercially managed species, such as hived
honeybees or alfalfa leaf-cutting bees. General stewardship of otherwise unmanageable local ground-nesting
bees on farms could also be beneficial. Over several years,
such stewardship practices could foster adequate
numbers of generalist bees to satisfy the pollination needs
of fields planted with this crop. In turn, these Cleome
species can feed diverse members of native bee communities on a farm, gradually multiplying their numbers to
pollinate additional native summer seed crops.
Ground-nesting bees comprise 90% of the individuals
and 80% of the species taken from C. lutea in the wild. This
bodes well for wild bee communities of the Intermountain
West amid postfire restoration seedings because progeny
of most of these ground-nesting bees should be deep
enough underground to survive the surface heat of wildfires. Seeded in the autumn during postfire rangeland
rehabilitation treatments, these Cleome species will germinate and bloom in the following summer, and their nectar
and pollen will feed surviving members of mid-summer
bee communities at a time when most seeded perennials
will often still be in vegetative growth stages. As both
Cleome species attract a diverse array of bees and set prodigious seed, a land manager’s choice will be guided by
an individual Cleome species’ geographic range and its
habitat requirements, particularly soil texture and moisture, rather than any difference in value for wild bee
communities.
Acknowledgments
Faye Rutishauser, Melissa Weber, Morgan Yost and James
McDonald contributed ably to all facets of the field and
laboratory work. Terry Griswold kindly shared label data
from bee surveys of the Grand Staircase region of southern Utah and Harold Ikerd assisted with database
searches. Dr Hugh Iltis enthusiastically shared his
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No claim to original US government works
158 J . H . C A N E
research insights for the Cleomaceae. I am especially
grateful to Drs Vincent Tepedino and Nancy Shaw for
their thorough and constructive critiques. This research
was funded by the Great Basin Native Plant Selection and
Increase Project through the USDI-BLM Great Basin Restoration Initiative and the USDA-FS Rocky Mountain
Research Station.
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Journal compilation © 2008 The Society for the Study of Species Biology
No claim to original US government works
Plant Species Biology 23, 152–158