J. AMER. SOC. HORT. SCI. 126(3):262–268. 2001.
Variation in Floral Induction Requirements of Hibiscus sp.
Ryan M. Warner1 and John E. Erwin2
Department of Horticultural Science, University of Minnesota, 1970 Folwell Ave., Saint Paul, MN 55108-6007
ADDITIONAL INDEX WORDS. Malvaceae, flower initiation, flower diameter, branching, irradiance, photoperiod, temperature
ABSTRACT. Thirty-six Hibiscus L. species were grown for 20 weeks under three lighting treatments at 15, 20, or 25 ± 1.5 °C
air temperature to identify flowering requirements for each species. In addition, species were subjectively evaluated to
identify those species with potential ornamental significance based on flower characteristics and plant form. Lighting
treatments were 9 hour ambient light (St. Paul, Minn., November to May, 45 °N), ambient light plus a night interruption using
incandescent lamps (2 µmol·m–2·s–1; 2200 to 0200 HR), or ambient light plus 24-hour supplemental lighting from high-pressure
sodium lamps (100 µmol·m–2·s–1). Five day-neutral, six obligate short-day, six facultative short-day, three obligate long-day,
and one facultative long-day species were identified. Fifteen species did not flower. Temperature and lighting treatments
interacted to affect leaf number below the first flower and/or flower diameter on some species. Hibiscus acetosella Welw. ex
Hiern, H. cisplatinus St.-Hil., H. radiatus Cav., and H. trionum L. were selected as potential new commercially significant
ornamental species.
Hibiscus is the largest genus in the Malvaceae family (250 to 300
species; Bates, 1965). Hibiscus sp. are primarily tropical in origin,
although several species are native to temperate and warm temperate regions (Table 1). Although the genus is quite large, only H.
rosa-sinensis L. (Chinese hibiscus), H. syriacus L. (Rose-of-Sharon),
H. moscheutos L., and hybrids developed by crossing H. coccineus
(Medic.) Walt., H. laevis All., and H. moscheutos are grown
commercially as ornamental plants.
Cultivated Hibiscus are known for their large flowers that range
in color from yellow to white and shades of pink and red. Flower
diameter of some herbaceous perennial cultivars can be up to 30 cm
(R. Warner, personal observation).
Commercially grown Hibiscus are both day-neutral (H. rosasinensis) (Dole and Wilkins, 1999) and long-day plants [H. syriacus
(Thomas and Vince-Prue, 1997), H. moscheutos (Runkle et al.,
1996)]. Hibiscus coccineus flowers naturally in July (Bates, 1965),
suggesting that it may also be a long-day plant. Hibiscus hiernianus
Exell & Mend., H. mastersianus Hiern., and H. mechowii Garcke
are short-day plants (Menzel et al., 1986). However, little information is available on the floral induction requirements of Hibiscus
species not commercially cultivated.
The popularity of Hibiscus presently being cultivated suggests
other Hibiscus sp. may have commercial potential as ornamental
plants. Therefore, the objectives of this research were to 1) determine environmental requirements for flowering of Hibiscus sp. and
2) identify potentially significant new ornamental species. Environmental treatments were selected to cover a wide range of thermoand photoperiodic possibilities to maximize the number of species
that would be induced to flower.
Materials and Methods
Seeds of 36 Hibiscus sp. (Table 1) were soaked for 12 h in ≈75
ºC water that was allowed to cool to room temperature (≈22 ºC)
(Nau, 1996) on 23 Nov. 1996. The experiment was repeated on 24
Received for publication 25 Feb. 2000. Accepted for publication 28 Dec. 2000.
Minnesota Agricultural Experiment Station scientific journal series paper 981210042.
The authors wish to acknowledge the Minnesota Commercial Flower Growers
Association, Minnesota Agricultural Experiment Station, Minnesota Extension
Service, Widmer Fund, and Ohio Floriculture Foundation for financial support of
this project. The cost of publishing this paper was defrayed in part by the payment
of page charges. Under postal regulations, this paper therefore must be hereby
marked advertisement solely to indicate this fact.
1
Graduate research assistant.
2
Associate professor.
Oct. 1997. Seeds that did not imbibe after soaking were scarified
manually. Seeds were then sown in 25-mL cells in a soilless
media (Germination Mix, Strong-Lite Horticultural Products,
Pine Bluff, Ark.) and covered with ≈2 to 4 mm of vermiculite
(Premium Grade Medium Vermiculite, Strong-Lite Horticultural
Products). Planting depth of each species varied and was ≈1.5
times the minimum diameter of a seed. Seeds were germinated
under intermittent mist (6 s of mist every 10 min, from 0700 to
1800 HR daily) at 23 ± 1 ºC air temperature. Seedlings were
removed from the mist and transplanted into 450-mL pots in a
soilless media (Universal Mix, Strong-Lite Horticultural Products)
when cotyledons were parallel to the media surface (≈2 to 3 d after
emergence from the media). Transplanted seedlings were then
placed in a greenhouse maintained at 20 ± 1 oC air temperature under
ambient daylight conditions (December 1996; November 1997; St.
Paul, Minn.) for 7 d, after which seedlings were moved and
environmental treatments were initiated.
Environmental treatments consisted of combinations of three air
temperature treatments (15, 20, or 25 ± 1.5 ºC), and three lighting
treatments. Lighting treatments within each temperature were:
short-day (SD; 9 h of ambient light, plants covered with opaque
black cloth daily from 1700 to 0800 HR; temperature under the black
cloth was not recorded), night-interruption [NI; ambient daylight
plus 2 µmol·m–2·s–1 irradiance from 2200 to 0200 HR, using incandescent lamps (Sylvania Directlite 100W, GTE Products Corp., Salem,
Mass.)], or continuous lighting [CT; ambient daylight plus continuous 100 µmol·m–2·s–1 supplemental lighting from high-pressure
sodium lamps (Lucolux LU400, General Electric, Cleveland, Ohio)].
Plants were fertilized weekly with 14.3 mM N, 0 mM P, and 6.5 mM
K, supplied by Ca(NO3)2 and KNO3. Every fourth week, plants were
fertilized with 14.3 mM N, 0.72 mM P, 6.5 mM K, 1.67 mM Ca, 1.1
mM Mg, plus trace amounts of micronutrients (Peter’s Excel 15N–
2.2P–12.5K Cal–Mg, The Scott’s Co., Marysville, Ohio).
Data were collected at anthesis or after 20 weeks on leaf number
below the first flower, plant height (from the media surface to the
apical meristem), height to the first flowering node, first flower
diameter, lateral shoot number (lateral shoots ≥2.5 cm), and visible
flower bud number (≥1 cm in length). Plants with visible flower
buds after 20 weeks remained in environmental treatments until
anthesis. Potential commercial ornamental significance was evaluated subjectively based on floral characteristics, including flower
size, flower color, flower number, whether plants flowered continuously, leaf and stem characteristics, and overall plant architecture.
The experiment was replicated twice over time, with each
treatment consisting of four plants per replicate. Plants were
completely randomized within each lighting/temperature treatment combination. Means were separated using Tukey’s HSD test
(P < 0.05) using the SPSS statistical analysis program (SPSS,
Inc., 1997).
Results
FLOWER INDUCTION AND DEVELOPMENT. Lighting and temperature treatments interacted with species to affect leaf number
below the first flower. For some species there were insufficient
plants for all treatments, so plants were placed in the 20 and 25 ºC
temperature treatments, or under SD and NI in the 20 ºC temperature treatment only (Tables 2 and 3). Fifteen species did not
flower under any environmental treatment (Table 1). All species
that flowered had a single flower in each leaf axil. Six species, H.
acetosella, H. cannabinus, H. engleri, H. mastersianus, H.
nigricaulis, and H. schinzii flowered with a lower leaf number
under the SD lighting treatment than under the NI lighting
treatment (Table 2).
Hibiscus asper, H. meeusei, H. physaloides, H. sabdariffa, and
H. surattensis flowered only under the SD lighting treatment
(Tables 2 and 3). Hibiscus radiatus flowered under the SD
lighting treatment at all three temperatures, but flowered under NI
lighting only when grown at 15 ºC (Tables 2 and 3). Hibiscus
surattensis flowered with a similar leaf number below the first
flower when grown under the SD or CT lighting treatments
(Table 2), but did not flower when grown under the NI lighting
treatment.
Species that flowered at 20 ºC regardless of lighting treatment
were H. calyphyllus, H. cisplatinus, H. costatus, H. lunarriifolius,
and H. meraukensis (Tables 2 and 3). These species flowered with
a similar leaf number below the first flower under either the SD
or NI lighting treatments.
Hibiscus aculeatus, H. laevis, and H. moscheutos required a
photoperiod inductive for flowering to grow, i.e., for continued
Table 1. Hibiscus sp., source, native range, and native range latitude of species evaluated in this experiment.
Species
H. acetosella Welw. ex. Hiern
H. aculeatus Walt.
H. arnhemensis F.D. Wilsony
H. arnottianus A. Grayy
H. asper Hook f.
H. biseptusy
H. calyphyllus Cav.
H. cannabinus L.
H. cisplatinus St.-Hil.x
H. coccineus Walt.y
H. costatus A. Richx
H. denudatus Benth.y
H. diversifolius Jacq.y
H. dongolensis Caill. ex Del.xy
H. engleri Schumannx
H. fallax Craven & F.D. Wilsony
H. furcellatus Desr.y
H. greenwayi Baker f.y
H. laevis All.
H. lunariifolius Willd.x
H. mastersianus Hiernx
H. meeusei Exell
H. meraukensis Hochr.
H. moscheutos L.
H. mutabilis L.y
H. nigricaulis Baker f.x
H. physaloides Guill.
H. radiatus Cav.
H. rostellatus Guill. & Perr.y
H. sabdariffa L.
H. schinzii Gurke.x
H. surattensis L.
H. taiwanianay
H. tiliaceus L.y
H. trionum L. Sunnyday
H. zonatus F. Muell.y
zUSDA
Source
PIz 260997
Commercial
PI 585151
Commercial
PI 585165
Commercial
PI 364895
Commercial
PI 372212
Commercial
PI 265239
Commercial
PI 263965
PI 364899
PI 364901
PI 595768
PI 585122
PI 405056
Commercial
PI 369345
PI 585154
PI 344232
PI 585121
Commercial
Commercial
PI 585155
PI 364904
PI 585159
PI 344219
PI 500741
PI 500714
PI 585138
Commercial
Commercial
Commercial
PI 585136
Native
range
Angola
Florida to Louisiana and North Carolina
N. Territory, Australia (Wilson, 1974)
Hawaii, endemic to Oahu
Collected in Uganda
S. Arizona and New Mexico (Rickett, 1970)
Tropical and South Africa
Probably Tropical Africa
Argentina, Paraguay, Uruguay, and S. Brazil
Georgia and S. Florida
Cuba, Mexico, C. America (Menzel et al., 1983)
California to Texas and Northern Mexico
Africa and Asian Tropics
Collected in South Africa
Collected in South Africa
Collected in N. Territory Australia
West Indies, Central, and South America, Hawaii
Collected in Kenya
Eastern United States
Collected in Uganda
Collected in Zambia
Collected in Zambia
Western Australia (Wilson, 1974)
Eastern United States
Probably S. China and Taiwan
Collected in Zambia
Collected in South Africa
Asian Tropics
Central Africa (Menzel and Wilson, 1963)
Probably Tropical Africa
Southern Africa
Central Africa (Menzel and Wilson, 1963)
China
Old and New World Tropics
Widespread in Europe, Africa, Asia, and Australia
N. Territory, Australia (Wilson, 1974)
plant introduction (PI) number.
did not flower under any environmental treatment in this experiment.
xSeeds were scarified manually.
ySpecies
Approximate
latitude (o)
6–17 S
30–35 N
12–25 S
23 N
4 N–2 S
30–33 N
0–30 S
23 N–23 S
23–33 S
28-33 N
12–23 N
30–35 N
23 N–23 S
23–32 S
23–32 S
12–25 S
0–25 N
4 S–4 N
27–42 N
2 S–4 N
8–18 S
8–18 S
15–35 S
27–42 N
20–30 N
8–18 S
23–32 S
0–23 N
10 S–20 N
23 S–23 N
10–30 S
10 S–20 N
20–40 N
23 S–23 N
12–25 S
Table 2. Effect of temperature and lighting treatment on leaf number below the first flower of Hibiscus sp. Species are grouped into the appropriate
photoperiodic response group. Numerals in parentheses represent leaf number at the end of the experiment on plants that did not flower. Plants
were grown under 9 h ambient light (St. Paul, Minn., from November to May) (SD), ambient light plus a 2 µmol·m–2·s–1 night interruption using
incandescent lamps from 2200 to 0200 HR (NI), or ambient light plus 100 µmol·m–2·s–1 continual supplemental lighting from high pressure sodium
lamps (CT).
Air
Species
temp (ºC)
Leaf no.
SD
20
25
15
20
20
20
25
20
25
20
17zayAx
15 aA
17 aA
25 aB
10 a
7 aA
12 aB
6 aA
10 aB
8a
15
20
25
20
25
20
25
15
20
25
15
20
25
15
20
25
7A
7A
23 B
6A
7A
15 A
24 aB
11 aA
16 aA
11 aA
Dead
8A
7A
Dead
10 aA
13 aB
H. calyphyllus
H. cisplatinus
H. costatus
H. lunariifolius
H. meraukensis
20
20
20
20
20
15 a
21 a
9a
13 a
9a
H. trionum
15
20
25
7 aA
16 cB
22 cC
H. aculeatus
20
25
20
25
15
20
25
Dead
Dead
gct
gc
gc
gc
gc
H. acetosella
H. cannabinusv
H. engleri
H. mastersianus
H. nigricaulis
H. schinzii
H. asper
H. meeusei
H. physaloides
H. radiatusu
H. sabdariffa
H. surattensis
H. laevis
H. moscheutos
zNumerals
NI
Facultative short-day
38 bA
47 bB
26 bA
34 bB
19 b
10 bA
23 bB
12 bA
22 bB
13 b
Obligate short-day
(18)
(20)
(25)
(17)
(21)
(22)
(27)
21 b
(31)
(41)
Dead
(16)
(21)
Dead
(20)
(31)
Day neutral
13 a
21 a
9a
13 a
9a
Facultative long-day
8 aA
10 bB
11 bB
Obligate long-day
28 aB
22 aA
24 aA
25 aA
23 A
24 aA
23 aA
CT
37 b
naw
27 bA
38 bB
na
14 c
(38)
17 cA
24 bB
na
(21)
(20)
(26)
na
na
(24)
(29)
24 bA
32 bB
(45)
Dead
(16)
(19)
(9)
10 aA
13 aB
15 a
21 a
na
na
8a
7 aA
6 aA
6 aA
33 aB
25 aA
24 aA
24 aA
na
25 aA
24 aA
represent treatment means.
yLower case letters indicate mean separation within a species and temperature, across lighting treatment, by Tukey’s studentized range test, P < 0.05.
xUpper case letters indicate mean separation within a species and lighting treatment, across temperature, by Tukey’s studentized range test, P < 0.05.
wPlants
were not grown in this treatment.
became too tall to maintain in 25 °C treatments.
uFacultative short-day plants at 15 °C.
tGrowth ceased after plants unfolded ≈10 leaves.
vPlants
Table 3. Effect of temperature and lighting treatment on days to first open flower of Hibiscus sp. Species are grouped into the appropriate
photoperiodic response group. Plants were grown under 9 h ambient light (St. Paul, Minn., from November to May) (SD), ambient light plus a
2 µmol·m–2·s–1 night interruption using incandescent lamps from 2200 to 0200 HR (NI), or ambient light plus 100 µmol·m–2·s–1 continual
supplemental lighting from high pressure sodium lamps (CT).
Air
Species
Days to first open flowr
temp (ºC)
SD
20
25
15
20
20
20
25
20
25
20
103zayBx
69 aA
166 aB
145 aA
57 a
40 aA
41 aA
46 aA
45 aA
60 a
15
20
25
20
25
20
25
15
20
25
20
25
20
25
66 B
52 A
109 C
54 B
43 A
59 A
70 B
119 aC
88 aA
60 A
74 B
56 A
71 aB
53 aA
H. calyphyllus
H. cisplatinus
H. costatus
H. lunariifolius
H. meraukensis
20
20
20
20
20
155 a
144 a
82 a
61 a
97 a
H. trionum
15
20
25
110 cA
109 cA
107 cA
H. aculeatus
20
25
20
25
15
20
25
Dead
Dead
gcs
gc
gc
gc
gc
H. acetosella
H. cannabinusv
H. engleri
H. mastersianus
H. nigricaulis
H. schinzii
H. asper
H. meeusei
H. physaloides
H. radiatust
H. sabdariffa
H. surattensis
H. laevis
H. moscheutos
zNumerals
NI
Facultative short-day
159 bA
152 bA
195 bB
177 bA
85 b
49 bA
63 bB
67 bA
92 bB
89 b
Obligate short-day
dnfu
dnf
dnf
dnf
dnf
dnf
dnf
175 b
dnf
dnf
dnf
dnf
dnf
dnf
Day neutral
167 a
147 a
86 a
66 a
101 a
Facultative long-day
92 bC
79 bB
68 bA
Obligate long-day
160 aB
131 bA
135 aB
119 aA
133 C
112 aB
99 aA
CT
155 b
naw
192 bB
169 bA
na
52 b
na
75 bA
94 bB
na
dnf
dnf
dnf
na
na
dnf
dnf
177 bB
122 aA
dnf
dnf
dnf
68 aA
47 aA
160 a
141 a
na
na
98 a
61 aC
43 aB
36 aA
151 aB
99 aA
131 aB
115 aA
na
105 aB
90 aA
represent treatment means.
yLower case letters indicate mean separation within a species and temperature, across lighting treatment, by Tukey’s studentized range test, P < 0.05.
xUpper case letters indicate mean separation within a species and lighting treatment, across temperature, by Tukey’s studentized range test, P < 0.05.
wPlants
were not grown in this treatment.
became too tall to maintain in 25 °C treatments.
uPlants did not flower in this treatment.
tFacultative short-day plants at 15 °C.
sGrowth ceased after plants unfolded ≈10 leaves.
vPlants
Table 4. Comparison of flower color and diameter of 21 Hibiscus sp.
grown under the lighting treatment that resulted in earliest flowering
at 20 ºC.
Species
H. acetosella
H. aculeatus
H. asper
H. calyphyllus
H. cannabinus
H. cisplatinus
H. costatus
H. engleri
H. laevis
H. lunariifolius
H. mastersianus
H. meeusei
H. meraukensis
H. moscheutos
H. nigricaulis
H. physaloides
H. radiatus
H. sabdariffa
H. schinzii
H. surattensis
H. trionum ‘Sunnyday’
Flower color
(center color)
Yellow (maroon)
Yellow (maroon)
Yellow (maroon)
Yellow (red-brown)
Cream (maroon)
Pink
Pink
Yellow (brown)
Pink (maroon)
Yellow (maroon)
Yellow (maroon)
Yellow (maroon)
Light pink
White (maroon)
Yellow (maroon)
Yellow (maroon)
Maroon
Cream (maroon)
Yellow (red-brown)
Yellow (maroon)
Cream (maroon)
Flower diam
(mm)
83z hy
75 g
52 e
47 d
101 i
107 j
51 e
33 bc
82 h
64 f
55 e
24 a
30 b
124 k
24 a
68 f
74 g
47 d
35 c
37 c
43 d
zNumerals
yMean
represent species mean.
separation by Tukey’s Studentized range test, P < 0.05.
leaf unfolding (Tables 2 and 3). For instance, growth of H. laevis
and H. moscheutos ceased under the SD lighting treatment after
plants unfolded about 10 leaves. Hibiscus aculeatus plants (roots
and shoots) died when grown under the SD lighting treatment,
regardless of temperature. Plants of all three species flowered
only under the NI or CT lighting treatments. Leaf number below
the first flower was similar under NI or CT for all three species.
Hibiscus trionum ‘Sunnyday’ had six leaves below the first
flower bud, regardless of the light/temperature treatment. However, the first flower buds aborted under SD and NI treatments at
20 and 25 ºC, resulting in variation in leaf number below the first
flower to develop completely to anthesis and days to anthesis
(Tables 2 and 3). For instance, plants grown under the CT lighting
treatment had about six leaves below the first flower to open
regardless of temperature. Similarly, plants grown at 15 ºC had
about seven leaves below the first flower to open regardless of the
lighting treatment. However, plants grown at 20 or 25 ºC had a
lower leaf number below the first flower to open when grown
under the CT lighting treatment than when grown under the NI or
SD lighting treatments. Similarly, plants grown at 20 or 25 ºC had
a lower leaf number below first flower to open when grown under
the NI than the SD lighting treatment.
Temperature interacted with lighting treatment to affect leaf
number below the first flower and days to anthesis on H.
cannabinus, H. mastersianus, H. nigricaulis, and H. physaloides
(Tables 2 and 3). For instance, leaf number of H. mastersianus
below the first flower when grown under the SD lighting treatment was 7 and 12 leaves on plants grown at 20 and 25 ºC,
respectively. Similarly, H. mastersianus plants grown under the
NI lighting treatment unfolded 10 and 23 leaves before forming
a flower at 20 and 25 ºC, respectively.
FLOWER COLOR AND DIAMETER. Flowers of 12 of the 21 species
that flowered were yellow with maroon, or sometimes brown,
centers (Table 4). Other flower colors observed were pink, white,
and maroon. Flower diameter at 20 ºC under the lighting treatment that resulted in earliest flowering for each species ranged
from 24 mm for H. meeusei and H. nigricaulis, to 124 mm for H.
moscheutos (Table 4).
Temperature interacted with lighting treatment to affect flower
diameter of two species, H. radiatus and H. nigricaulis. H.
radiatus flower diameter under the SD lighting treatment at 15,
20, and 25 ºC was 31, 72, and 100 mm, respectively. Increasing
temperature from 20 to 25 ºC increased H. nigricaulis flower
diameter from 24 to 54 mm under SD.
LATERAL SHOOT NUMBER AND PLANT HEIGHT . Hibiscus
sabdariffa, H. surattensis, and H. trionum were the only species
with lateral shoots. Increasing temperature increased the number
of lateral shoots for all three species when grown under the CT
lighting treatment (Table 5). For example, H. surattensis had 0,
4, and 7 lateral shoots under CT at 15, 20, and 25 ºC, respectively.
In contrast, H. surattensis plants had a similar number of lateral
shoots under all three lighting treatments at 20 ºC. However,
plants grown at 25 ºC had 2, 6, and 7 lateral shoots when grown
under the SD, NI, and CT lighting treatments, respectively.
Species, lighting treatment, and temperature interacted to affect
Table 5. Effect of lighting and temperature treatment on lateral shoot number of three Hibiscus sp. Lighting treatments: 9 h ambient light (St. Paul,
Minn., from November to April) (SD); ambient light plus 2 µmol·m–2·s–1 from 2200 to 0200 HR (NI), or ambient light plus 100 µmol·m–2·s–1
continuous light (CT).
Lateral shoot no.
Species
H. sabdariffa
H. surattensis
H. trionum ‘Sunnyday’
zNumerals
Temp (ºC)
15
20
25
15
20
25
15
20
25
SD
Dead
1zayAx
0 aA
Dead
4 aB
2 aA
5 bA
5 bA
7 bA
NI
Dead
5 bA
7 bB
Dead
4 aA
6.0 bB
3 bA
2 aA
4 aA
CT
Dead
4 bA
8 bB
0A
4 aB
7 bC
2 aA
3 aB
5 aB
represent treatment mean.
yLower case letters indicate mean separation across lighting treatment, within a species and temperature, by Tukey’s studentized range test, P < 0.05.
xUpper case letters indicate mean separation across temperature, within a a species and lighting treatment, by Tukey’s studentized range test, P <
0.05.
plant height at anthesis (Table 6). For instance, H. asper height at
anthesis was 247, 332, and 789 mm under SD when grown at 15, 20,
and 25 ºC, respectively. Height of H. radiatus at anthesis at 15 ºC
was 217, 342, and 506 mm under SD, NI, and CT, respectively. Plant
height at anthesis across all treatments ranged from 150 mm for H.
costatus to 1500 mm for H. acetosella (Table 6).
Discussion
Fifteen species did not flower in any treatment after 20 weeks
(Table 1). This is not surprising considering many of these species
are shrubs or trees in their indigenous habitats and may have a
juvenile period longer than the length of the experiment (Salisbury
and Ross, 1992).
Variation in the photoperiodic requirement for flower induc-
tion among Hibiscus sp. studied herein is consistent with results
reported for other Hibiscus sp. (Menzel et al. ,1986; Thomas and
Vince-Prue, 1997; Wilkins and Kotecki, 1982) and other genera,
including Allium L. and Coleus Lour. (Thomas and Vince-Prue,
1997). For instance, interrupting a 15 h night ≥1 h with a low
irradiance (1 to 3 µmol·m–2·s–1 from incandescent lamps) induced
90% of a H. moscheutos ‘Disco Belle Mixed’ population to
flower (Runkle et al., 1998). Results herein support the classification of H. moscheutos as a long-day plant. However, subsequent work we conducted indicated H. moscheutos ‘Disco Belle
Pink’ is an obligate long-day plant only when daily light integral
is ≤13 mol·m–2·d–1 (Warner, 1999). Hibiscus moscheutos ‘Disco
Belle Pink’ is a facultative long-day plant when daily light
integral is ≥13 mol·m–2·d–1 under a 9 h photoperiod.
Our classification of H. cannabinus, H. mastersianus, H.
Table 6. Effect of temperature and lighting treatment on plant height (mm) at anthesis of 17 Hibiscus sp. Plants were grown under 9 h ambient light (St.
Paul, Minn., from November to May) (SD), ambient light plus 2 µmol·m–2·s–1 from 2200 to 0200 HR (NI), or ambient light plus 100 µmol·m–2·s–1
continuous light (CT).
Air
Species
H. acetosella
H. aculeatus
H. asper
H. calyphyllus
H. cisplatinus
H. costatus
H. engleri
H. laevis
H. lunariifolius
H. mastersianus
H. meeusei
H. meraukensis
H. moscheutos
H. nigricaulis
H. physaloides
H. radiatus
H. sabdariffa
H. schinzii
H. surattensis
zNumerals
temp (ºC)
20
25
20
25
15
20
25
20
20
20
20
20
25
20
20
25
20
25
20
15
20
25
20
25
20
25
15
20
25
20
25
20
20
25
Plant ht (mm)
SD
488zayAx
494 aA
dnf
dnf
247 A
332 A
789 B
256 a
485 a
150 a
289 a
dnf
dnf
263 a
909 aA
1079 aB
172 A
230 A
162 a
dnf
dnf
dnf
222 aA
523 aB
729 A
814 B
217 aA
528 C
369 B
176 A
198 A
181 a
307 aA
570 bB
NI
946 bA
1500 bB
578 aA
895 aB
dnf
dnf
dnf
256 a
507 a
273 b
278 a
527 aA
672 bB
310 a
972 bA
1338 bB
dnf
dnf
272 b
522 A
611 bB
637 bB
409 cA
633 aB
dnf
dnf
342 b
dnf
dnf
dnf
dnf
183 a
dnf
dnf
CT
568 a
dnfw
668 aA
790 aB
dnf
dnf
dnf
244 a
477 a
---v
--551 aA
611 aB
--915 a
dnf
----285 b
--545 aA
563 aA
348 bA
1072 bB
dnf
dnf
506 c
dnf
dnf
dnf
dnf
--280 aA
479 bB
represent treatment mean.
yLower case letters indicate mean separation within a species and temperature, across lighting treatment, by Tukey’s studentized range test, P < 0.05.
xUpper case letters indicate mean separation, within a species and lighting treatment, across temperature, by Tukey’s studentized range test, P < 0.05.
wPlants
vPlants
did not flower in this treatment.
were not grown in this treatment.
sabdariffa, and H. surattensis as short-day plants is consistent
with previous results (Crane, 1949; Crane and Acuna, 1945;
Menzel et al., 1986). Hibiscus surattensis flowered under both
SD and CT, but flowering was completely inhibited by NI.
Inhibition of flowering by NI, but not SD or CT, has been reported
for other short-day plants, including H. sabdariffa (El-Afry et al.,
1980; Mansour, 1975). However, for results presented herein, H.
sabdariffa did not flower when grown under CT. Similarly,
Cockshull (1979) reported that three cultivars of the short-day
plant, Dendranthema ×grandiflorum Kitam. (syn. Chrysanthemum ×morifolium Ramat.) (chrysanthemum), initiated flower
buds when grown under continuous light. However, flower buds
of only one of the three cultivars, ‘Golden Stardust’, developed to
anthesis, and only when the temperature was 10 or 16 ºC.
The photoperiodic response for flowering of a given species is
closely linked to the indigenous habitat of that species. Plants
from latitudes 30 to 55 ºN are often long-day plants that may or
may not require vernalization (Roberts and Summerfield, 1987).
This ensures that plants will flower and produce seed during the
warm summer months before going dormant for the winter. In
contrast, plants from latitudes of 0 to 30 ºN are often short-day
plants or day-neutral (Roberts and Summerfield, 1987). Our
results are consistent with observations of Roberts and
Summerfield (1987) where Hibiscus sp. native to the United
States (i.e., H. militaris and H. moscheutos) were obligate longday plants. In contrast, species native closer to the equator (i.e.,
H. calyphyllus, H. cannabinus, and H. radiatus) were day-neutral
and short-day plants (Tables 1 and 2).
High temperature treatment (25 oC) delayed flowering of some
Hibiscus sp. under inductive lighting treatments (Tables 2 and 3).
For example, increasing temperature from 20 to 25 °C increased
leaf number below the first flower on H. mastersianus and H.
nigricaulis, i.e., developmental delay. In contrast, increasing
temperature from 20 to 25 °C increased leaf number below the
first flower and days to anthesis on H. asper and H. physaloides,
i.e., developmental delay and delay in time. In all cases, Hibiscus
sp. that exhibited high temperature delay in flowering eventually
flowered. Interestingly, species that exhibited high temperature
delay were among facultative or obligate short-day plant groups
only.
High temperature inhibition or delay of flowering has been
observed in other species. Short-day induced flower initiation in
Euphorbia pulcherrima Willd. ex Klotzsch. (poinsettia) is delayed when night temperature exceeds 22 °C (Dole and Wilkins,
1999). Similarly, short-day induced flowering in Dendranthema
×grandiflorum and Schlumbergera truncata (Haw.) Moran.
(Thanksgiving cactus) is delayed when day or night temperature
exceeds 22 °C (Karlsson et al., 1989; Erwin et al., 1990). Pharbitis
nil Chois. flowering is delayed (Reese and Erwin, 1997) and
Pelargonium ×hortorum L.H. Bail. (geranium) flower number
per inflorescence decreases as average daily temperature increases (Erwin and Heins, 1993).
Based on subjective characteristics mentioned previously, we
determined that H. cisplatinus and H. radiatus have potential as
new commercial ornamental crops. Hibiscus acetosella and H.
trionum are currently commercially available, but are not widely
grown.
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