Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 November 2021 | 13(13): 20056–20065
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
https://doi.org/10.11609/jott.6741.13.13.20056-20065
#6741 | Received 24 September 2020 | Final
received 16 September 2021 | Finally accepted 20 October 2021
Reproductive biology of Ophiorrhiza caudata
C.E.C.Fisch. (Rubiaceae), an
endemic and endangered creeping perennial herb of the Western Ghats, India
Maria Theresa 1, Appukuttan Kamalabai Sreekala 2 & Jayalakshmi Mohanlal 3
1–3 Division of Conservation Biology,
Jawaharlal Nehru Tropical Botanic Garden and Research Institute, Pacha-Palode, Thiruvananthapuram, Kerala 695562, India.
1 mariavempally@gmail.com, 2 ak.sreekala@gmail.com
(corresponding author), 3 jeevaa88@gmail.com
Editor: Cleofas Cervancia,
University of Philippines Los Bayos College Laguna,
Philippines. Date of publication: 26
November 2021 (online & print)
Citation: Theresa, M., A.K. Sreekala & J. Mohanlal (2021). Reproductive biology of Ophiorrhiza caudata
C.E.C.Fisch. (Rubiaceae),
an endemic and endangered creeping perennial herb of the Western Ghats, India. Journal of Threatened Taxa 13(13): 20056–20065. https://doi.org/10.11609/jott.6741.13.13.20056-20065
Copyright: © Theresa et al. 2021. Creative Commons Attribution
4.0 International License. JoTT allows unrestricted use, reproduction, and
distribution of this article in any medium by providing adequate credit to the
author(s) and the source of publication.
Funding: University of Kerala.
Competing interests: The authors
declare no competing interests.
Author details: Dr. Maria Theresa has been awarded PhD by the
University of Kerala. She joined as assistant professor (on contract) in the department of botany, Newman College, Thodupuzha, Idukki. Dr. A.K. Sreekala
is working as Principal scientist in the division of conservation biology,
JNTBGRI, Palode. She has published more than 85
research papers in national and international journals. Also presented 60 research papers in national and international
conferances. Dr. Jayalakshmi
Mohanlal has been awarded PhD by the University of Kerala and presently
she is working as guest lecturer in the department of botany, Vimala College
(Autonomous), Thrissur.
Author contributions: All the three authors contributed
equally for the study as well as MS preparation.
Acknowledgements: The authors are thankful to the
Director, KSCSTE-Jawaharlal Nehru Tropical Botanic Garden and Research
Institute for providing facilities and the Department of Forests and Wildlife,
Government of Kerala, special thanks to conduct study in the forest area. The
authors are thankful to the manuscript reviewers. The first author is thankful
to the University of Kerala, Thiruvananthapuram for providing Junior Research
Fellowship.
Abstract: Ophiorrhiza caudata is a creeping, perennial herb
distributed along wet and shady areas. The species is distylous
with two distinct floral morphs: pin and thrum. Flowering usually occurs during
the monsoon season. No particular difference was noticed in the flowering
phenology of the two morphs. Presently the species is self-incompatible,
however, it shows a tendency towards intramorph
compatibility. Fruit set is above 60% in open pollination and intermorph
pollination. Bees and butterflies are the major pollinators. The pollen flow
between the two floral morphs varies depending upon floral morphology and
pollinators. Fruit is a bi-valved capsule which
dehisces by a splashing drop mechanism. The seeds are very minute. The rate of
seed germination and seedling establishment in the wild condition is very poor
due to adverse climatic factors. Ophiorrhiza
caudata is struggling for survival in its natural
habitat, where habitat fragmentation, climatic factors and poor seedling
establishment could account for its narrow distribution.
Keywords: Floral morphs, flowering
phenology, perennial herb, pollination, seed germination.
INTRODUCTION
The genus Ophiorrhiza
L. (Rubiaceae) is believed to be Indo-Malaysian in
origin (Mabberly 2008), and different species are
scattered throughout tropical-subtropical Asia, New Guinea, Australia, and the
Pacific islands. The roots of these
herbaceous plants were used against snake venom from ancient times, and various
plant parts are characterised by the presence of the alkaloid camptothecin and its derivatives (Yamazaki et al. 2003). Camptothecin is an inhibitor of the enzyme topoisomerase-1
(Uday & Kondapi 2010) and has anti-cancerous
properties. Some Ophiorrhiza species such as O.
barnesii, O. brunonis
and O. incarnata are also under threat of
extinction due to climatic change, habitat disturbance, natural calamities and
obstruction to pollination mechanisms and reproduction.
The genus has been considered as distylous (Deb & Mondal 1977) with two floral morphs:
pin (long-styled) and thrum (short-styled). Distyly
is usually associated with self-incompatibility, that is, the flower of one
morph cannot be fertilized by the pollen from the same flower or from another
flower of same morph. This kind of heteromorphic incompatibility is reported
from 25 plant families including Rubiaceae (Ganders
1979; Lloyd & Webb 1992). Darwin (1877) considered distyly
as an adaptation to promote cross breeding. Ophiorrhiza
caudata C.E.C.Fisch.
is a creeping herb distributed along the wet and shady regions of southern
Western Ghats. The species was considered extinct (Deb & Mondal
1997), and IUCN (1997) included it under the extinct category. It was rediscovered
in 2009 (Joseph & Joseph 2009), 70 years after its last report. Considering
the medicinal value and present status of this endemic distylous
species, a study on its reproductive mechanism is needed for conservation. The
present investigation was carried out during 2013–2016 to examine the flowering
phenology, floral biology, breeding system, pollination and seed biology of O.
caudata.
MATERIALS
AND METHODS
Study area
A clumped population of O. caudata was located in the Mankulam
and Kallar forest areas of Idukki district (Image
1a) in Kerala (10011.9230”N
76092.884”E, 340–2,102 m). The average rainfall in the area ranges
from 2,500–3,000 mm, with 70% occurring during the south-west monsoon; mist and
frost prevail during the winter months and high humidity during the monsoon
season. O. caudata is distributed along the
wet and shady areas of Mankulam and Kallar (Figure 1). Ophiorrhiza mungos,
O. barberi, and O. barnesii are the other ophiorrhiza
species distributed along this area. Dictyospermum
montanum, Neanotis decipiens, Plectanthus malabaricus, Cleome speciosa,
Impatiens elegans, Impatiens maculata,
Cyanotis pilosa, and
Pilea melastomoides are other associated plants in
the area.
Phenology and floral morphology
Twenty-five healthy individuals
of approximately the same age from both floral morphs (i.e., pin and thrum)
were marked, and periodic observations were made on different developmental
events from the emergence of vegetative buds up to seed germination and
successful establishment of seedlings. The observations were made as per the
method suggested by Dafni (2007). The time of anthesis and anther dehiscence,
flower colour and odour, nectar production, stigma type, and flower longevity
were noticed. The flower morphology of each morph was studied with the help of
hand lens and dissection microscope. Floral measurements were taken in
millimetres by using a digital vernier calliper. For
this purpose, 20 flowers of each morph were collected from the field, preserved
in 70% ethanol and detailed study was conducted in the laboratory. This was
helpful to analyse heterostyly in the species.
The mean number of pollen grains
per flower was calculated by dissecting a single anther in a drop of
acetocarmine: glycerine (3: 1) on a microscopic slide and counting all the
grains; the number obtained was multiplied by five (the number of anthers per
flower). In this way the pollen count was taken from anthers of 10 flowers
(from 10 different individuals of each morph) and the mean number of pollen
grains per flower was calculated. The average number of ovules per ovary was
counted by dissecting young pistils under a microscope. Pollen-ovule ratio was
calculated as per the method suggested by Cruden
(1977).
Pollination biology
Field observations of flower
visitors were carried out from 0600 to 1630 h. Insect foraging activity was
noted by visual observation. Number of floral visits per hour by each
pollinator, their foraging behaviour, time spent by the insect on each flower
and stigma touch were recorded. Temporal activities of the insects on pin and
thrum morphs were distinctly noted.
Pollinators were trapped using
insect nets, pan traps and sticky traps (Toler et al. 2005). Trapped insects
were preserved individually in small screw cap vials (10 ml) containing 4 ml of
ethyl alcohol. The vials were vigorously shaken for two minutes to remove
pollen grains from the insect’s body. The insects were taken out from the vial
and the suspension was allowed to evaporate. After evaporation, pollen grains
were mounted in a few drops of acetocarmine-glycerin
stain and observed under a microscope. The number of stained and unstained
pollen grains of the selected plant species was counted. The pollinators were
identified with the help of entomologists from the school of biology, IISER,
Thiruvananthapuram, and an insect manual.
Breeding system
The mating system of the distylous species was analysed by fruit set comparisons in
the field after various breeding experiments such as self-pollination, intramorph pollination, intermorph pollination,
emasculation & bagging, and bagging without emasculation. Fruit set after
these experiments were compared with the fruit set after open pollination. For
each of the breeding experiment, 150 flowers were chosen from different
individuals. The results were compared with Student’s t-test. (SPSS ver.16.0 at
the significance level of α= 0.05)
Self-pollination was conducted to
check whether the species is self-compatible. For this, flower buds one day
before anthesis were bagged using butter paper bags and pollinated the next day
using pollen from flowers of the same individual. The pollinated flowers were
bagged again, and periodically observed for fruit set. For intramorph
pollination, flower buds were emasculated and bagged one day before anthesis
using butter paper bags. On the next day, pollen grains were transferred from
flowers of other individuals of the same morph into the opened flower. For
intermorph pollination, the flower buds were emasculated, bagged and were
pollinated with pollen grains from flowers of the other morph. Another set of
flowers were emasculated and bagged to check the occurrence of apomictic fruit
test. Several
flower buds were bagged without emasculation to test autogamous
self-pollination within each morph.
Fruit and Seed biology
Fruit development was observed
from the day of pollination until its maturation and dehiscence. Mature fruits
from each morph were harvested and seeds collected. The average number of seeds
developed per fruit/capsules was calculated. For analysing the reproductive
success of flowers after pollination, the number of flowers per day in a 10 x
10 m quadrate of the population and the number of mature fruits developed from
these flowers were scored and the flower-fruit ratio was calculated.
For the evaluation of seed
dispersal, laboratory experiments were preferred because the seeds of Ophiorrhiza were minute to count from the intact
soil. Peduncles with an open capsule containing mature seeds were placed in
individual bottles and set on a floor covered with three square meters of white
paper for easy detection of the scattered seeds. One 2 ml syringe fixed at a
height of 2 m and water drops were allowed to fall onto the open capsule. Each
water drop was approximately 0.1 ml. After the seeds scattered by water
droplets, the longest distance from the peduncle to the seed was measured. The
experiments were repeated at least five times for each morph (Nakanishi 2002).
For analysing seed germination,
mature fruits were covered with paper bags before dehiscence and seeds were
collected from each morph separately. Seeds were stored under laboratory
conditions and allowed to germinate in petri dishes under different conditions:
1) Whatman filter paper (Grade 1); 2) soil from natural habitat; 3) soil from
JNTBGRI campus. Samples of seeds were also allowed to germinate in the natural
habitat to assess the influence of environmental factors on seed germination.
Five replicates of 30 seeds of each morph were allowed to germinate every month
to determine the optimal month for seed germination and seedling establishment.
Quantitative features such as the number of days taken for seed germination and
percentage of seed germination and seedling establishment in the field as well
as in the laboratory conditions were analyzed
periodically.
RESULTS
Phenology and floral morphology
O. caudata is a perennial creeping herb
that sprouts at the end of May. Vegetative buds arise from the nodes of
creeping stems during the monsoon, and the young leaves are yellowish-green.
When mature, it becomes dark green in its upper surface and brownish green in the
lower surface. The plants started to bloom in June and continued to January
(Figure 2). New seedlings take 75–86 days to flower. Peak blooming was noticed
from mid-August to mid-September (Figure 2).
When the fruit matures, each fruit contains 45–110 minute brownish seeds
which are dispersed by rain water
The inflorescence of O. caudata is a terminal capitate cyme with 1–6 flowers,
with the flowers arranged in a centrifugal manner. Flower development completes
within 7–10 days (Image 1d). Anthesis was noticed in the morning hours between
0600–0845 h and anther dehiscence occurs soon after flower opening. Flowers of
thrum morphs open earlier than pin ones. Flowers are white with a mild
fragrance and the nectar is located on the semicircular
disc present above the ovary. Average
life span of each flower is 20–24 hours. Blooming lasts for an average of 215
days in a year. Fruit development was completed within 25-35 days after
pollination. During heavy rain, dehiscence of fruits occurs by splashing drop
mechanism.
The inflorescence and peduncles
are glabrous, and 2.5–3.5 cm long. The flowers are
white, lanceolate and 9.3–13.5 mm long. Pedicels are 1–1.5 mm long. Hypanthium
is cup shaped. Calyx lobes are 5, ovate-lanceolate, acute and shortly keeled at
back. Corolla is white and infundibuliform with 5 lobes. They are 8–10 mm long
and glabrous outside with a ring of hairs on the
throat of corolla tube. Stamens are 5 and are epipetalous; anthers are oblong
and longitudinally dehiscent. Average length of the stamen is different in the
two different morphs, 2.45 mm in pin flowers and 7.19
mm in thrum flowers. Ovary is obovoid, 0.59–0.85mm x 0.31–0.41 mm in pin flowers and 0.65–0.81mm x 0.33–0.41 mm in thrum
flowers. Style is slender in both morphs but its length varies among the two
different morphs, 5.95 mm in pin flowers and 1.79 mm
in thrum flowers. Stigma-bifid and capitate in pin
flowers and lanceolate in thrum flowers (Image 1b,c).
Pollination Biology
Butterflies, flies, bees and ants
were the major floral visitors of O. caudata,
and they were attracted by the mild fragrance of flowers. Flowering was in rainy season, and rainwater
promotes pollination (Hydrophily) in O. caudata.
One unidentified insect visits the flowers frequently; it spend around 45 ± 15 sec per flower in pin
morphs and 46 ± 21 sec per flower in thrum morphs (Figure 3, 4). This insect
either collects pollen from the exposed anthers of thrum flowers or enters the
corolla tube to collect nectar. In pin morph, they enter into the corolla tube
for collecting both pollen and nectar. Pollen flow into the thrum morphs by this insect was
comparatively poor because the stigma is positioned under the throat of the
corolla tube and therefore there was a reduced stigma touch. The prime floral
visitor was stingless bee
(Trigona iridipennis).
It can enter up to the throat of
the corolla tube and collects both pollen and nectar. The tiny fruit flies also
make irregular visits and collects nectar. Oriens
goloides is a butterfly visitor with more foraging
time comparing to the other butterflies. Eurema
blanda silhetana and Leptosia nina are the other butterflies
visiting on the same time (Figure 3, 4). However, they spend only less time per
visit but have more frequent visits per flower. These tiny butterflies make
frequent movements in the flower which facilitates cross-pollination.
Butterflies normally rest on the corolla, exert their proboscis and collect the
nectar present on the disc above the ovary. Therefore, the pollen transfer from
the inserted anthers of pin morph flowers into the stigma of thrum flowers
which is also located inside the corolla tube will be comparatively less.
Breeding System
Fruit set was not observed after
self-pollination, emasculation and netting, netting without emasculation
experiments in both the morphs. This indicated that the species was
self-incompatible and there is no apomixis or parthenocarpic
fruit development in this species. The
percentage of fruit set after intramorph pollination
in pin and thrum morphs are 6.67% and 3.33%, respectively. These results
indicated that O. caudata has a tendency
towards intramorph compatibility. Pin (female) x
Thrum (male) and Thrum (female) x Pin (male) crosses resulted in 72% and 69%
fruit set respectively and no notable difference between the morphs (t= 3.21, P
>0.05). Therefore, the male and female organs of both the morphs were
functional. Open pollination resulted in a fruit set of 66% in pin morphs and
64% in thrum ones. Comparison of these
results with the manual intermorph pollination treatments showed no notable
difference (Pin (female) x Thrum (male), inter-morph pollination vs. open
pollination, 72% vs. 66%, t= 4.33, P >0.05 and thrum (female) x pin (male),
inter-morph pollination vs. open pollination, 69% vs. 64%, t= 4.90, P >0.05)
(Table 1).
Fruit and seed biology
The fruit is a boat-shaped, bi-valved capsule which dehisces along the dorsal surface
(Image 1e). The capsule attains its maximum size (6.7 ± 0.51 mm x 5.4 ± 0.72 mm
in pin morphs and 6.7 ± 0.32 mm x 5.5 ± 0.63 mm in thrum morphs) within 25–35
days after pollination. Each fruit contains 86 ± 12 seeds in both morphs and
the number of seeds in the two locules may vary. The
seeds were minute (0.68 ± 0.06 mm x 0.54 ± 0.05mm in pin plants and 0.64 ± 0.07
mm x 0.58 ± 0.08 mm in thrum plants), angular, glabrous
and were brown coloured. Flower-fruit
ratio of pin morphs in natural condition was calculated as 1.5:1 and that of
thrum flowers was 1.6:1.
Seed dispersal
The seed dispersal mechanism in O.
caudata was splash seed dispersal by raindrops.
During rain, the water drops were collected in the boat-shaped capsule
containing the seeds, which are splashed out and flushed away over certain
distance. Thus the raindrops provide energy for the seeds to come out of the
capsule. The maximum dispersal distance of seeds under laboratory conditions in
pin morphs was 93 ± 5.9 cm and 93 ± 5.6 cm in thrum morph seeds.
Seed germination and seedling
establishment
The freshly harvested seeds of O.
caudata shows dynamic germination in all the
conditions, which indicates the seeds, are recalcitrant. Seed germination was
hypogeal. In both morphs, maximum seed germination 40–45 % was noticed within
2–4 weeks after harvest (Figure 5, 6; Image 1f). The rate of germination was noticed
to be declining in the next weeks. But the seedling establishment was at a
reduced level while comparing to the seed germination rate in the natural
habitat. This poor rate of seedling establishment may due to the heavy rain in
the fruiting season. In natural condition, during heavy rain, the minute seeds
are either buried in the mud or carried away by the rain water and only an
average of 25% seedlings were established in the wild. However, seeds
germinated in the plastic pots when transferred to the natural habitat also
failed to establish due to heavy rainfall. In the natural condition, about 3%
seeds inside the capsule exhibit viviparous germination which can be considered
as an adaptation for establishment of young seedlings during heavy precipitation.
DISCUSSION
The genus Ophiorrhiza
L. is characterised by white or pinkish white flowers and most of the species
exhibit heterostyly. Majority of the Ophiorrhiza
species reported from Western Ghats exhibit the similar pattern of flowering
except the varieties of O. brunonisis which
flowers during the summer months (Deb & Mondal 1997). Anthesis occurs in both the morphs in the early morning around
0600 h, and all the flowers completely open within around 0845 h. Distylous species with white tubular flowers in Rubiaceae such as Psychotria
carthagenesis (Consolaro
et al. 2011) follow the same pattern of anthesis. Simultaneous opening of
flowers of both the morphs have a positive influence on the pollen transfer
between them.
The family Rubiaceae
is characterised by different pollen transfer mechanisms and functional gender
of pin and thrum morphs with various pollination systems (Wolff & Liede-Schumann 2007). Several investigations were conducted
on the pollination biology of heterostylous plants in
Rubiaceae, and there are species which have evolved
functional dioecy in the family (Li et al. 2010). Flowering of O. caudata is during monsoon. The earlier studies (Wolda 1988; Fonseca et al. 2006; Silva et al. 2011)
reported highest foraging activities of Hymenoptera and Lepidoptera during the
rainy season. This observation agrees with the pollinators of candidate
species, and can be considered an adaptation to suitable conditions for
pollination, i.e., species tend to flower when vector availability is higher,
as reported in other plant groups (Almeida & Alves 2000; Koptur et al. 1988; Martin-Gajardo
& Morellato 2003).
The stingless bee Trigona iridipennis is a major pollinator of the
selected species. Pollination by Trigona was
observed in other members of Rubiaceae, including Psychotria barbiflora
(Texeira & Machado 2004) and Manettia cordifolia (Consolaro et al.
2005). They visit the flowers in morning immediately after anthesis. High level
of nectar concentration in morning hours stimulated the visit of Trigona spinipes in
both the morphs of Psychotria poeppigiana (Valois-Cuesta et al. 2009). In Ophiorrhiza, the nectar is present in trace
amounts and was too viscous in the selected species to be measured by
conventional hand refractometers. Trigona, the
tiny bees can enter into the corolla tube, feed pollen and nectar from both
morphs. Trigona and fruit flies can enter the
narrow corolla and comes in contact with the short stigma of thrum flowers but
other hymenopterans and lepidopterans are less able to enter the narrow corolla
tube of thrum morphs and moreover there is a ring of hairs along the corolla
tube above the stigma. If these hairs are absent, even short stigmas of thrum
flowers can effectively receive pollen grains from pin flowers (Stone &
Thomson 1995) Eurema blanda
silhetana and Leptosia
nina are the common butterflies visiting Ophiorrhiza caudata.
They usually visit the flowers after two hours of anthesis and there is a
competition between them for nectar. These restless butterflies spend less time
per flower but have frequent visits. Oriens
goloides and an unidentified butterfly from Hesperiidae visits O. caudata
for nectar. Butterflies usually alight near or on flowers when foraging for
nectar (Naiki & Kato 1999), and in Ophiorrhiza caudata they
took the exudates secreted from the disc above the ovary by extending their
proboscides into the corolla tube. Therefore, butterflies most often come in
contact with the exposed floral parts from the corolla tube; anthers of thrum
flowers and stigmas of pin flowers. Thus the pollen transfer from pin morphs to
thrum was comparatively poor. No significant difference was observed in the
foraging time, foraging period, and number of visits per flower and stigma
touch among the morphs of the selected species.
According to some authors, thrum
(short-styled) flowers are efficiently pollinated by insects with longer
mouthparts (Beach & Bawa 1980; Lloyd & Webb
1992), while short-tongued insects would be more efficient pollinators of pin
(long-styled) flowers (Beach & Bawa 1980). In
another view, reproductive interference might interrupt the proper functioning
of disassortative pollination between short-level organs, which promote
asymmetric pollen flow due to extremely narrow corollas of the species
pollinated by Lepidopterans (Marten-Rodriguez et al. 2013). Ophiorrhiza
caudata do not totally depend on lepidopterans
for their pollination; bees, fruit flies and even rain water act as pollinating
agents. Here, lepidopterans are efficient pollinators of pin morphs and
asymmetry in pollen flow by insect vectors is noticed because of the narrow
corolla tube. Fruit flies and Trigona can
enter the narrow corolla and comes in contact with the short stigma of thrum
flowers but other Hymenopterans and Lepidopterans are less able to enter the
narrow corolla tube of thrum morphs. There is a ring of hairs along the corolla
tube above the stigma. If these hairs are not present, even short stigmas of
thrum flowers can effectively receive pollen grains from pin flowers (Stone
& Thomson 1995). Even though the pollen grains from pin flowers were
attached to the proboscis of an insect, most of them would be easily swept off
by the hairs in a thrum flower, which results in asymmetric pollen flow between
the pin and thrum flowers (Naiki & Kato 1999).
When considering pollination by lepidopterans, some butterflies collect the
nectar without the stigma touch (Naiki & Kato
1999). However, these butterflies efficiently transfer pollen from the exposed
anthers of thrum flowers to the exposed stigmas of pin flowers with their
proboscis and other mouthparts or with legs and wings.
Manual pollination treatments
confirmed that the species is self-incompatible and no fruits are developed by
apomixis. After interpreting the results of illegitimate pollination, it is
found that a small percentage of fruit set is obtained after intra-morph
crossing. This indicates that the species shows a tendency towards intra-morph
compatibility. Heterostylous species are usually
self- and intra-morph incompatible and produce fruits only after legitimate
(intermorph) pollination. However, self- and intra-morph compatibility was
reported from both distylous (Ornduff
1976) and tristylous (Barrett 1985; Eckert &
Barrett 1994) species. Intra-morph compatibility accompanied by
self-incompatibility is reported from tristylous Narcissus
triandrus (Barrett et al. 1995) in Amaryllidaceae, from the distylous
Anchusa hybrid (Dulberger,
1970), and from Anchusa officinalis (Philipp
& Schou, 1981) in Boraginaceae.
In Rubiaceae, partial intramorph
compatibility was reported from several self- incompatible distylous
species like Psychotria nuda
(Castro & Araujo 2004), P. homalosperma (Watanabe et al. 2014) and Gaertnera vaginata (Pailler & Thompson 1997) where fruit set was obtained
after illegitimate pollination in one morph and no fruit set in the other one. Intramorph incompatibility may gradually decrease in the
species and may become intramorph and self-compatible
in the future. The heterostylous species which are
self-compatible were considered to be derived from self-incompatible ancestors
(Baker 1966; Ganders 1979).
Fruit of O. caudata is a bi-valved
capsule which dehisces along the dorsal surface. According to Deb & Mondal
(1997), many seeded dehiscent fruit of Ophiorrhiza
which releases and disperses seeds is a primitive character while comparing to
the few seeded indehiscent fruit. Flower-fruit ratio in the two morphs
specifies that above 60% fruit set was obtained in natural conditions. Seed
dispersal mechanism is splash or ballistic seed dispersal by rain drops in
which the seeds are dispersed into the surroundings due to the pressure exerted
by the rain drops falling in the loculicidal capsule. This kind of seed
dispersal was reported in O. japonica in which the seeds are dispersed
to a maximum distance of 95.0 ± 6.2 cm (Nakanishi 2002). Nakanishi (2002)
reported the same mechanism of seed dispersal in Sagina
spp. (Caryophyllaceae), Sedum spp. (Crassulaceae), Gentiana
spp. (Gentianaceae) and several members of Saxifragaceae and Scrophulariaceae.
All these plants are herbaceous and splash rain dispersal might be an advantage
for small plants because dispersal is not affected by plant height. Occasionally,
in the absence of rain, the seeds of Ophiorrhiza
sp. are dispersed by wind.
The minute seeds of Ophiorrhiza showed maximum seed germination
within 2–4 weeks after the harvest. The
seeds of Ophiorrhiza caudata
showed more than 40–45 % germination in all the conditions, but only a few
seedlings are establishing in the wild habitat. In natural conditions, most of
the seeds are leached along with the rain water or buried in the muddy soil.
The germinating seeds were also destroyed by heavy rain. There is increasing
evidence that the events which occur during seedling establishment influences
the distribution and abundance of
adults in a
plant community (Marks
1974; Platt 1975;
Werner 1977; Rabinowitz
1978; Gross & Werner 1982). Seeds leached out by the rain water
which may germinate in a long distance apart which leads to habitat
fragmentation.
CONCLUSION
Ophiorrhiza caudata is an endangered species endemic
to the southern Western Ghats. It exhibits heterostyly, but shows some
deviations from the typical characters of a heterostylous
species. Its breeding system is self-incompatible but shows some degree of
intra-morph compatibility, which has an evolutionary significance. Poor
seedling establishment in wild conditions, habitat fragmentation, and
anthropogenic activities are the major threats for the survival of the species.
Only 25% of seedlings were established in the wild condition due to climatic
problems. The seedlings were successfully established in Jawaharlal Nehru
Tropical Botanic Garden and Research institute campus. Conservation of this
rediscovered medicinal plant is of great significance in the present scenario.
The self-incompatible heteromorphic species which is phasing environmental and
other threats in its natural habitat is conserved in our campus. Both the
morphs are protected, thereby promote cross pollination and further
establishment of the species.
Table 1. Percentage of fruit set in six pollination methods in pin
and thrum morphs of Ophiorrhiza caudata.
|
Treatment |
Number of flowers examined |
Fruit set (%) |
1 |
Self-pollination |
|
|
|
Pin |
150 |
00 |
|
Thrum |
150 |
00 |
2 |
Intramorph pollination |
|
|
|
Pin x Pin |
150 |
6.67 |
|
Thrum x Thrum |
150 |
3.33 |
3 |
Intermorph pollination |
|
|
|
Pin (female) x Thrum(male) |
150 |
72. 51 |
|
Thrum(female) x Pin(male) |
150 |
69. 07 |
4 |
Emasculation and netting |
|
|
|
Pin |
150 |
00 |
|
Thrum |
150 |
00 |
5 |
Netting without emasculation |
|
|
|
Pin |
150 |
00 |
|
Thrum |
150 |
00 |
6 |
Open pollination |
|
|
|
Pin |
150 |
66. 76 |
|
Thrum |
150 |
64. 13 |
For figures
& images - - click here
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