Journal of Threatened Taxa | www.threatenedtaxa.org | 26 July
2019 | 11(9): 14119–14127
Pollination ecology of Brownlowia tersa (Malvaceae), a Near Threatened non-viviparous true mangrove shrub
Aluri Jacob Solomon Raju
Department of Environmental Sciences, Andhra
University, Visakhapatnam, Andhra Pradesh 530003, India.
solomonraju@gmail.com
doi: https://doi.org/10.11609/jott.4906.11.9.14119-14127
Editor: Cleofas Cervancia,
University of Philippines Los Baños College Laguna,
Philippines. Date
of publication: 26 July 2019 (online & print)
Manuscript details: #4906 | Received 18 February
2019 | Final received 31 May 2019 | Finally accepted 16 June 2019
Citation: Raju, A.J.S. (2019). Pollination ecology of Brownlowia tersa (Malvaceae), a Near Threatened non-viviparous true mangrove
shrub. Journal of Threatened Taxa 11(9): 14119–14127. https://doi.org/10.11609/jott.4906.11.9.14119-14127
Copyright: © Raju 2019. Creative Commons Attribution
4.0 International License. JoTT allows unrestricted use, reproduction, and
distribution of this article in any medium by adequate credit to the author(s) and
the source of publication.
Funding: UGC, New Delhi, India and Society for Conservation Biology, Washington
DC, USA.
Competing interests: The author declares no competing
interests.
Author details: Prof. A.J. Solomon Raju is the recipient of several national and
international awards. He has more than 300 research papers in international and
national Journals.
Acknowledgements:
The work reported in this paper
was carried out with the financial support received under BSR Mid-Career Award
instituted by the University Grants Commission, New Delhi, and Marine Section -
Small Grants Program instituted by the Society for Conservation Biology,
Washington DC, USA.
Abstract: Brownlowia tersa is a low-ground semi-evergreen shrub species. The phenological events occur
sequentially—leaf fall, leaf flushing, flowering and fruiting from April to
November. It is hermaphroditic,
protandrous, self-compatible, facultative xenogamous,
and melittophilous involving worker honey bees, small
male and female carpenter bees and male and female cuckoo bees. Of these, worker honey bees and female
carpenter bees forage for both pollen and nectar while male carpenter bees and
both sexes of cuckoo bees forage exclusively for nectar. Cuckoo bees are very important for cross-pollination
because they are swift fliers and visit many flowers from different plants in
the shortest time. Carpenter bees and
honey bees are largely important for self-pollination as they are not fast
fliers and tend to spend more time at each flower for forage collection. The flowers have a specialized pollination
mechanism to resort to autonomous autogamy if not pollinated but this mode of
pollination is subject to the availability of pollen in its own anthers. Fruit is a 1-seeded follicle produced from a
single carpel of the flower. It is
indehiscent and floats in tidal water when detached from the plant. When settled in muddy substratum, it breaks
open to expose the seed which germinates and produces a new plant in quick
succession. The study reports that the
plant is highly threatened due to different human economic activities taking
place in the area and hence immediate in situ conservation measures are
required for its protection and propagation.
Keywords: Facultative xenogamy, hermaphroditism, melittophily.
INTRODUCTION
The Malvaceae family
contains herbs and shrubs (Tang et al. 2007).
Flowers of this family are usually hermaphroditic and entomophilous (Ruan 2010). Wind
pollination in the species of this family is unlikely because the pollen grains
are sticky and tend to clump together.
Pollinators are mostly bees and butterflies; however, other pollinators
are species-specific and include hawk moths, hummingbirds, and other birds (Rathcke 2000; Ruan 2010). In this family, the sub-family Brownlowioideae consists of eight genera with 70 species
distributed in palaeo-tropical latitudes. This sub-family is characterized by sepals
fused into a campanulate tube (Burret 1926), many
stamens either unfused or slightly fused into fascicles at their base with or
without staminodia (Ridley 1922; Hutchinson 1967),
and ovaries sessile or borne on a short-stalk representing gynophore. Among these genera, Brownlowia
consists of about 30 species widely distributed in southeastern
Asia through Malaysia and the Pacific Islands (Tomlinson 1986). Different authors reported that Brownlowia is a genus of trees, comprising about 25
species in southern and southeastern Asia with Borneo
as centre of its distribution where it is represented by 17 species of which 15
are endemics. Many species of this genus
grow along rivers, in swamp forests and mangroves (Kostermans
1965; Turner 1995; Bayer & Kubitzki 2003). This genus is distinguished from other genera
by its apocarpous fruits and loosely connected
carpels (Bayer & Kubitzki 2003). Only two shrub hermaphroditic species B. argentata and B. tersa
have been reported as occurring in swamp forests and river banks, and mangroves
inundated by the highest tides (Tomlinson 1986). These two species have been classified as
true mangrove species by different authors (Duke 1992; Giesen
et al. 2007; Polidoro et al. 2010). B. tersa is
distributed from India to southeastern Asia where it
has been recorded in Myanmar, Cambodia, Thailand, Malaysia, Brunei, Singapore,
the Philippines, Indonesia (Giesen et al. 2007). In India, its distribution is restricted to
the east coast where it is common in West Bengal and Odisha but rare in the
Godavari estuary of Andhra Pradesh, and the Andaman & Nicobar Islands (Venu et al. 2006; Kathiresan
2010; Bhatt et al. 2011). This species
is distinguishable in the field based on certain characters such as the
presence of brown-scaly twigs, lanceolate leaves with dull silvery undersurface and pear-shaped, 2-valved fruits. It often grows in stands along the banks,
remains almost half-submerged during high tide, and withstands the tidal surges
due to its intricate root system.
Globally, it is reported as a true mangrove species (Duke 1992; Giesen et al. 2007; Polidoro et
al. 2010) though it has not been included in the Indian mangrove flora in
certain national and international status reports (Kathiresan
& Bingham 2001; Kathiresan & Rajendran 2005;
Anonymous 2008; Mandal & Naskar 2008). But, it is reported as a true mangrove
species in the mangrove flora of Andaman & Nicobar Islands (Sahni 1958; Debnath 2004).
In the IUCN Red List, it is included in the Near Threatened category (Kathiresan 2010; Polidoro et al.
2010) and the reasons stated for this status include habitat loss from coastal
development, erosion and the construction of shrimp and fish ponds throughout
its range. Further, it is also stated
that this species may qualify for threatened category in the near future due to
its occurrence only on the landward margin where it is the most vulnerable to
coastal development and human activities (Kathiresan 2010). B. tersa has
been in use as a traditional folk remedy for diarrhoea, dysentery, wounds and
boils. Roots possess antibacterial
activity while leaves possess anti-inflammatory, antioxidant, analgesic and
anti-diarrhoeal activities (Hossain et al. 2013). Despite its threatened status, there have
been no studies on the reproductive biology of this species in any part of its
distribution. Further, the other species
B. argentata has also not been investigated
for its reproductive biology so far.
Tomlinson (1986) noted that the pollination biology of Brownlowia is unknown. Since then, no one has ever attempted to
report on the pollination biology of any species of this genus.
The study is aimed at providing certain details of
floral biology and pollination in B. tersa
which is currently in threatened status at Coringa
Mangrove Forest (CMF), Andhra Pradesh, India.
This information is useful to understand the sexual, breeding, and
pollination systems and fruiting ecology.
Further, it provides clues to understand why it attained threatened
status not only at this forest and also at other mangrove forests where it is
distributed.
MATERIALS AND METHODS
CMF covering an area of 188km2
lies at 16043’47.413”N and 82012’54.864”E. It is located in the delta in East Godavari
District; it is created by the river Godavari.
Freshwater flows into the mangrove wetlands of the Godavari delta for a
period of six months and peak flow normally occurs during July to September,
coinciding with the southwest monsoon season.
During this period the entire delta, including the mangrove wetland is
submerged under freshwater, since penetration of sea water is completely
blocked by the large amount of incoming freshwater. Brackish water conditions prevail from
October to February and sea water dominates the entire mangrove wetland from
March to May due to the absence of freshwater discharge. In recent times, however, freshwater
discharge from the river system is low due to insufficient and erratic rainfall
during monsoon seasons.
Field studies were carried on
the populations of Brownlowia tersa (L.) Kosterm. in the areas of Ratikalva
Reserve Forest which falls under non-sanctuary area of CMF. Observations regarding the organization of
inflorescences, the spatial positioning of flowers, and their position on the
plant were made since these features are regarded as important for foraging and
effecting pollination by flower-visitors.
The flower longevity was recorded by marking 20 just open flowers and
following them until fall off. Anthesis
was initially recorded by observing 10 marked mature buds in the field. Later, the observations were repeated five
times on different days, each day observing 10 marked mature buds in order to
provide accurate anthesis schedule. The
same marked mature buds were followed for recording the time of anther
dehiscence. The presentation pattern of
pollen was also investigated by recording how anthers dehisced and confirmed by
observing the anthers under a 10x hand lens.
The details of flower morphology such as flower sex, shape, size,
colour, odour, sepals, petals, stamens and ovary were described.
Twenty-five mature but
un-dehisced anthers were collected from five randomly chosen plants and placed
in a petri dish. Later, each time a
single anther was taken out and placed on a clean microscope slide (75 x 25 mm)
and dabbed with a needle in a drop of lactophenol-aniline-blue. The anther tissue was then observed under the
microscope for pollen, and if pollen grains were not there, the tissue was
removed from the slide. The pollen mass
was drawn into a band, and the total number of pollen grains was counted under
a compound microscope (40x objective, 10x eye piece). This procedure was followed for counting the
number of pollen grains in each anther collected. Based on these counts, the mean number of
pollen produced per anther was determined.
The characteristics of pollen grains were also recorded. The stigma receptivity was observed by H2O2
test as given in Dafni et al. (2005).
The presence of nectar was
determined by observing 50 mature buds and open flowers collected at random
from 10 plants. Individual volumes of
nectar were recorded for 20 flowers and then the average volume of nectar per
flower was determined and expressed in µl.
The flowers used for this purpose were bagged at the mature bud stage,
opened after anthesis and nectar squeezed into micropipettes to measure the
volume of nectar. Nectar sugar
concentration was also simultaneously determined using a hand sugar
refractometer (Erma, Japan).
Fifty flowers each from 10
randomly selected plants were used for each mode of the breeding system. The
stigmas were pollinated with the pollen of the same flower manually by using a
brush; they were bagged for fruit set through manipulated autogamy. The flowers were fine-mesh bagged without
hand pollination for fruit set through spontaneous autogamy. The emasculated flowers were hand-pollinated
with the pollen of a different flower on the same plant; they were bagged and
followed for fruit set through geitonogamy.
The emasculated flowers were pollinated with the pollen of a different
individual plant and bagged for fruit set through xenogamy. All these modes of
pollination were followed for one month for calculating the percentage of fruit
set in each mode. Twenty inflorescences
consisting of 125 flowers were tagged on 20 plants prior to anthesis and
followed for fruit set rate in open-pollinations. Fruit maturation period, fruit dehiscence,
seed dispersal and establishment were observed in detail.
The insects visiting the flowers
were bees only and they had their nesting sites close to B. tersa populations.
They were observed carefully for 10 hours a day for 15 days in different
weeks during the flowering season. The
hourly foraging visits of each bee species were recorded on 10 different days
for which 30 inflorescences were selected.
The data obtained was used to calculate the percentage of foraging
visits made by each bee species per day in order to understand the relative
importance of each bee species.
Simultaneously, the bees were observed for their foraging behavior such as mode of approach, landing, probing
behaviour, the type of forage they collected, contact with essential organs to
result in pollination, and inter-plant foraging activity. The bees were captured from the flowers
during 10.00–12.00 h on five different days for pollen analysis in the
laboratory. For each bee species, 10
specimens were captured and each specimen was washed first in ethyl alcohol and
the contents stained with aniline-blue on a glass slide and observed under a
microscope to count the number of pollen grains present. In the case of pollen collecting bees, pollen
loads on their corbiculae/scopae were separated prior
to washing them. From pollen counts, the
average number of pollen grains carried by each bee species was calculated to
know the pollen carryover efficiency of different bees.
RESULTS
Habit and phenology
Brownlowia tersa is a semi-evergreen bushy and spreading shrub
distributed in sunny locations along tidal creeks and brackish water creeks
where mud is accreting (Image 1a). A
green snake (unidentified) uses the habitat of this plant in all locations
where the plant occurs (Image 1b,c). It
grows up to two meters in height without any above ground roots. It is fast growing, much-branched and forms
pure stands. The branches are grey,
smooth and marked with lines and grooves along their length. Leaves are petiolate, lanceolate to
elliptic-lanceolate and leathery with a rounded base and a pointed tip; the
upper surface is glossy and smooth while the lower surface is grey-green and
covered with a dense layer of tiny, hairy scales. Leaf fall occurs during late April to late
May, leaf flushing during June–July and flowering during late July to second
week of September at population level.
Individual plants flower for about four weeks only. Inflorescence is terminal and axillary; it is
a paniculate cyme with several flowers which open over a period of about a
week. (Image 1e,f). Cauliflorous
flowers are also borne on main stems and woody trunks.
Flower morphology
Flowers are pedicellate, 5–7 mm long, 5-6 mm wide,
creamy-brown coloured, mildly odoriferous, bisexual and actinomorphic. Calyx is bell-shaped, 5-sepalled, connate
below and light yellow with brown dots all over. Corolla is cream-coloured with light yellow
base, 2–3 mm longer than calyx, 5-petalled, free and apex rounded. Stamens are many, free, present in five
bundles and free from calyx and corolla.
Anthers are petaloid and attached to the filament by the base. Ovary sits on a well-developed stalk. It has four carpels which are partially
joined and each carpel has two reniform ovules (Image 2k–n). All four carpels are joined by a common style
tipped with a simple stigma.
Floral biology
Mature buds are globose and open during 09.00–11.00 h
with peak opening at 10.00h (Image 2a–g).
The stamens show anther dehiscence by longitudinal slits during
anthesis. In mature buds, the stigma is
below the height of stamens but stands straight and erect beyond the height of
the anthers during anthesis. The stigma
remains so for 6 hours and gradually curves towards the anthers of the same
flower and eventually contacts its own pollen.
It attains receptivity three hours after anthesis and remains so for
five hours. The pollen grains are
oblate-spheroidal, yellow, 3-colporate, sexine
thinner than nexine and 27–29 μm
in size (Image 2h–j). They are initially
sticky but later turn powdery with a gradual increase in temperature and fall
as single grains. Individual anthers
produce 890.6 ± 52.83 pollen grains and the total pollen output by a flower
depends on the number of stamens produced.
The stigma terminates its receptivity by the end of the day. Nectar is produced in minute volumes around
the base of the carpels and is protected by the basally connate calyx; it
amounted 1.2 ± 0.23 µl per flower and the sugar concentration stood at 28 ±
1.5%. The flowers fall off by noon of
the second day.
Breeding systems
Hand-pollination tests showed that the plant produces
fruit through self and cross-pollination.
Fruit set rate varied from 14–34 % in unmanipulated and manipulated
autogamy, 50% in geitonogamy, 72% in xenogamy and 34% in open-pollination. These results indicate that fruit set is the
highest in xenogamy and lowest in unmanipulated autogamy among hand-pollination
tests. Fruit set evidenced in
open-pollination is taken as the product of auto-, geitono-
and xeno-gamy (Table 1).
Flower visitors and pollination
The flowers were foraged exclusively by bees during
09.00–17.00 h with peak activity during 10.00–13.00 h coinciding well with the
availability of more fresh flowers (Fig. 1).
The bees belong to Apidae family and included
honey bees (Apis cerana
F. and A. florea F.), a small carpenter bee (Ceratina binghami Cockerell) and a cuckoo bee (Thyreus
histrio F.; Image 1d). In honey bees, only worker bees visited the
flowers and foraged for both pollen and nectar.
Worker bees collected pollen, groomed and brushed it down towards the
hind legs and packed the pollen into the corbiculae or pollen baskets which are
located on the tibia of the same legs.
They used nectar collected by them for their own consumption and also
for feeding the queen and male bees of the hive nearby in the same forest. In other bee species, both male and female
bees visited the flowers. The male
carpenter bee foraged for only nectar while female bee foraged for both pollen
and nectar. The male carpenter bee
collected nectar for its own consumption while female carpenter bee used the
nectar collected by it for its own consumption and also mixed it with pollen to
make bee bread to feed the larvae. The
female carpenter bee collected pollen and packed it as honey bees did but they
packed it into the weak scopa surrounded by sparse body hairs located on the
tibia of hind legs. The male and female
cuckoo bees foraged for only nectar for their own consumption. The floral architecture facilitated the bees
to probe for the forage with great ease and during probing they contacted the
stigma and stamens effecting pollination.
Worker honey bees and the female carpenter bees tended to spend more
time at each flower, plant and patch as they were involved in collecting both
pollen and nectar while male carpenter bees and both sexes of cuckoo bee tended
to spend less time at each flower, plant and patch as they were involved in
collecting only nectar. All four bee
species made inter-plant and inter-patch flower visits in quest of more forage
and in the process they effected both self- and cross-pollinations. Among all four bee species, T. histrio made 26%, A. florea
and C. binghami, each 25% and A. cerana 24% of total visits recorded at the flowering
patch (Fig. 2). The pollen recorded in
body washings of sampled specimens of bees indicated that all of them carry and
transfer pollen to other flowers either in the same or different patches. The average number of pollen grains recorded
was 115.4 for A. cerana, 99.1 for A. florea, 98.1 for C. binghami
and 162.3 for T. histrio (Table 2).
Fruiting ecology and seed dispersal
In fertilized flowers, calyx remains for about a week
without any further development and falls off subsequently. A single carpel produces fruit in fertilized
flowers. Fruits mature in about four
weeks; remain greyish-green from fruit initiation and until dispersed (Image
2o,p). Individual fruit is a woody,
fibrous heart-shaped follicle, 12–15 mm long and bi-lobed with a single
seed. It is indehiscent while on the
plant, falls off when due, floats due to its fibrous husk of fruit carpel, imbibition
of water by it; this floating state of fruits facilitated their dispersal by
tidal water. When it settles on the
muddy substratum and upon imbibition, it breaks open exposing the seed but
fruit carpel remains intact until seed germination. With initiation of root growth and development,
the cotyledons shed the fruit carpel and show continued growth to form
seedlings and subsequently new plants (Image 2q–s).
DISCUSSION
Brownlowia tersa is a shrubby, spreading plant
and forms patchy distribution along the tidal creeks connecting the landward
zone at the study area. An unidentified
green snake has been found to use this gregarious shrub at all locations of its
occurrence for its shelter but why it uses the habitat of this particular plant
is unknown. In B. tersa,
flowering and fruiting seasons are variously reported by different
authors. Kathiresan
(2010) noted that it flowers and fruits during July–October but he has not
mentioned the location where it was recorded.
Ragavan et al. (2016) noted that it flowers
during February–March and fruits during April–July in India and Andaman &
Nicobar Islands. The present study made
at CMF India showed that all phenological events occur sequentially—leaf fall,
leaf flushing, flowering, and fruiting—from April to November. Flowering starts in late July and continues
for about seven weeks while fruiting during October–November at population
level, however, individual plants flower for less than a month. The flowers are borne in terminal and
axillary paniculate cymes as well as on main stems and woody trunks indicating
that the plant with shrubby habit perhaps evolved to compensate the brief
period of flowering by producing cauliflorous flowers
in order to attract pollinators and maximize fruit set at plant level.
Different authors provided
taxonomic characters of B. tersa but certain
characters have been incorrectly reported.
Judd & Manchester (1997) reported that Brownlowia
flowers have five elongate antipetalous staminodia while Chung & Soepadmo
(2017) noted that B. tersa flowers have lanceolate
staminodes and persistent androgynophore. The present study showed that B. tersa lacks staminodia and androgynophore but it has gynophore on which the ovary is
well seated. Further, the stamens are
bundled, anthers petaloid which dehisce by longitudinal slits, and the carpels
with reniform ovules are partially joined by a common style terminated with a
simple stigma. The floral details of B.
tersa clearly indicate that the plant is
morphologically and functionally hermaphroditic. Protandry and the erect position of the
stigma above the anthers facilitate the occurrence of only geitonogamy and
xenogamy for a brief period; in addition, vector-mediated autogamy also occurs
upon the commencement of stigma receptivity.
Finally, the flowers resort to autonomous autogamy by gradually curving
the style and stigma towards the anthers; this pollination mode is a “fail-safe”
strategy evolved by the plant to ensure pollination in flowers that have not
been pollinated by pollinator bees. Its
occurrence, however, is subject to the availability of pollen in the anthers of
the same flower. Ruan
et al. (2010) reported on style curvature and its role in effecting self-pollination
in 52 species of Malvaceae. These authors classified the studied species
into two types: species with style curvature before pollen shedding, and
species with style curvature after pollen shedding. In the former type, the styles remain erect
if stigmas are pollinated or cease to curve if pollination occurs in the
process of style curvature or continue to curve downwards towards the anthers
if not pollinated. In the latter type,
the styles curve eventually bringing stigmas down to establish contact with the
anthers. The style curvature and
eventual occurrence of self-pollination in B. tersa
represents the second type, sensu Ruan
et al. (2010). Therefore, B. tersa is a perfect hermaphroditic species with
facultative xenogamous mating system.
Ruan (2010) stated that anemophily
is unlikely in Malvaceae because the pollen grains
are sticky. Spira
(1989) reported that H. moscheutos with sticky
pollen grains is not anemophilous and a vector other than wind is needed for
successful pollination. The present
study shows that B. tersa pollen is also
sticky and in effect, the bees foraging on the flowers collect pollen slowly
indicating that the plant is not anemophilous.
Further, the sticky nature of the pollen enables the plant to avoid
anemophily during non-receptive phase of the stigma to maximize
cross-pollination and minimize self-pollination. Feng (1984) and Rachcke
(2000) reported that many species of Malvaceae are
entomophilous and pollinated by bees, butterflies, hawk moths and birds. Faegri & van
der Pijl (1979) and Proctor et al. (1996) reported
that bee-pollinated flowers vary in their size, shape and colouration; they may
be open and bowl-shaped (radially symmetrical) or more complex and non-radially
symmetric (zygomorphic), and offer nectar and pollen as rewards. The present study reports that B. tersa displays a radially symmetrial
flower shape, dull-coloured corolla, mildly odoriferous and also offers nectar
and pollen as rewards to pollinators; in line with this, the plant is pollinated
exclusively by bees and hence it is melittophilous. Among bees, Apis
spp. carry pollen in pollen baskets located on their hind legs for use
subsequently by their colony while female bees of C. binghami
carry pollen in the scopae located on their hind legs
for brood provisioning. The pollen
collection activity by these bees significantly decreases pollen availability
for pollination purpose although pollination is effected by them, and also it
mostly undermines the occurrence of autonomous autogamy towards the end of the
day. The production of many flowers in
paniculate cymes, on main stem and woody trunk daily, individual flowers with
several stamens and each stamen producing copious pollen appear to enable the
plant to compensate the pollen loss caused by Apis
and C. binghami bees, however. Male bees of C. binghami
and both sexes of T. histrio act exclusively
as nectar feeders and play principal role in the pollination of B. tersa. Further, T.
histrio is a swift flier, collects nectar from as
many flowers as it could in a single visit and hence is very important in
effecting cross-pollination. Apis bees build their colonies on the peripheral
branches of Excoecaria agallocha
while C. binghami has its nests in the stems
of Acanthus ilicifolius; these plant species
occur 5–10 m away from B. tersa. T. histrio
does not have its own nest but it uses the underground nests of Amegilla sp. which occur nearby on the landward side
of the mangrove forests. Since the nests
of all these bee species occur near B. tersa,
they display a situation of floral constancy and effect pollination due to
massive flower production by the plant during the flowering season.
In the present study,
hand-pollination tests on B. tersa indicated
that the plant is self-compatible and fruits through all modes of pollination
with varying levels of reproductive success, however, fruit set rate in
open-pollinations is not commensurate compared with the ability of the plant to
fruit through autogamy with or without involvement of pollinators and through
geitonogamy and xenogamy with the involvement of pollinators. Further, the flowers characteristically
produce 1-seeded fruits only from a single carpel indicating that only one out
of four carpels forms fruit and only one of 2-ovules of the carpel forms
seeds. The fruits are indehiscent and
float in tidal water upon detachment from the plant. Different authors noted that Brownlowia species are often dispersed by
water indicating that they float in tidal water (Kostermans
1965; Turner 1995; Bayer & Kubitzki 2003). Similarly, Rachmadiyanto
et al. (2017) reported that B. peltata also
produces 1-seeded fruits from a single carpel but the fruits dehisce into
carpels to expose the seeds; the fruits float and disperse by water. The fruits of B. tersa
float because fruit pericarp is fibrous and imbibe water. Since the locations of the plant are situated
towards landward zone, the fallen fruits do not disperse longer distances and
soon they settle in muddy substratum.
Gradually, the seed inside the fruit imbibes water and breaks the fruit
open exposing the seed which soon germinates and produces a seedling and then a
new plant. The fruit pericarp, however,
remains enclosing the cotyledons until the initiation of root formation by the
seedling. Similar process of fruit
floating and seed germination is reported in B. peltata
by Rachmadiyanto et al. (2017).
Gopal & Chauhan (2006) noted
that B. tersa populations are experiencing
severe loss at the range margins due to human activities and coastal
development and hence has become an endangered species in India while Kathiresan (2010) mentioned that B. tersa
is Near Threatened. Field studies
conducted in this mangrove forest area for the last 12 years for the
reproductive ecology information on different mangrove plant species showed a
gradual decrease in the population size of B. tersa
due to deforestation and modification for fuel wood collection, cattle shelter
and eco-tourism activities. This
situation is to be corrected otherwise this species would face the risk of
genetic erosion and become extirpated in the course of time. Therefore, immediate and effective in situ
conservation measures are necessary for its protection and propagation.
CONCLUSIONS
Brownlowia tersa is a low-ground semi-evergreen
shrubby species. It displays
phenological events sequentially—leaf fall, leaf flushing, flowering, and
fruiting—from April–November. It is
hermaphroditic, protandrous, self-compatible, facultative xenogamous
and melittophilous.
It has the ability to fruit with or without pollinator activity but
fruit set rate is the highest with pollinator activity. Pollinators are exclusively bees consisting
of honey bees, small carpenter bees, and cuckoo bees of which the last one is
very important for cross-pollination due to their swift flying behavior and ability to collect nectar from many flowers of
different plants. Fruit is a 1-seeded
follicle and produced from a single carpel of the flower. It is indehiscent and floats in tidal water
when detached from the plant. When
settled in muddy substratum, it breaks open to expose the seed which germinates
and produces a new plant. The study
reports that the plant is highly threatened due to land use changes and regular
human and cattle activity, and hence immediate in situ conservation measures
are required for its protection and propagation.
Table 1.
Results of breeding systems in Brownlowia
tersa.
Pollination mode |
No. of flowers pollinated |
No. of fruits formed |
Fruit set (%) |
Autogamy (unmanipulated) |
50 |
7 |
14 |
Autogamy (manipulated) |
50 |
17 |
34 |
Geitonogamy |
50 |
25 |
50 |
Xenogamy |
50 |
36 |
72 |
Open-pollination |
125 |
43 |
34 |
Table 2. Pollen recorded in the body washings of
insect foragers on Brownlowia tersa.
Insect
species |
Sample
size (N) |
Range |
Mean |
S.D. |
Apis cerana |
10 |
54–208 |
115.4 |
50.08 |
Apis florea |
10 |
93–156 |
99.1 |
19.44 |
Ceratina smaragdina |
10 |
95–129 |
98.1 |
12.23 |
Thyreus histrio |
10 |
67–304 |
162.3 |
75.49 |
For
figures & images – click here
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