Journal of
Threatened Taxa | www.threatenedtaxa.org | 26 May 2025 | 17(5): 26973–26984
ISSN 0974-7907 (Online) | ISSN 0974-7893 (Print)
https://doi.org/10.11609/jott.9424.17.5.26973-26984
#9424 | Received 17 September 2024 | Final received 29 April 2025 |
Finally accepted 08 May 2025
Pollen morphology of Annonaceae from the Bicol
Region, Philippines
Anne O. Retuerma-Dioneda 1 & Grecebio
Jonathan D. Alejandro 2
1,2 The Graduate School, University
of Santo Tomas, España, Manila 1015, Philippines.
1 Department of Biology, College of
Science, Bicol University, Legazpi City, Philippines.
2 College of Science and Research
Centre for the Natural & Applied Sciences, University of Santo Tomas, España, Manila 1015, Philippines.
1 ardioneda@bicol-u.edu.ph
(corresponding author), 2 gdalejandro@ust.edu.ph
Editor: Cleofas R. Cervancia,
University of Philippines Los Baños College Laguna,
Philippines. Date of publication: 26 May 2025
(online & print)
Citation: Retuerma-Dioneda,
A.O. & G.J.D. Alejandro (2025).
Pollen morphology of Annonaceae from the Bicol
Region, Philippines. Journal of Threatened Taxa 17(5): 26973–26984. https://doi.org/10.11609/jott.9424.17.5.26973-26984
Copyright: © Retuerma-Dioneda
& Alejandro 2025. 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: Commission on Higher Education (CHED), Bicol University and University of Santo Tomas, Graduate School.
Competing interests: The authors declare no competing interests.
Author details: Anne O. Retuerma-Dioneda is a graduate of doctor of philosophy major in biology at the University of Santo Tomas, Manila.
She is also an associate professor V at the Bicol University College of Science, Legazpi City. She has expertise in plant science, systematics, taxonomy, and biodiversity conservation. Grecebio Jonathan D. Alejandro is a professor V at the College of Science and currently the Director of the Office for Graduate Research, Graduate School, University of Santo Tomas (UST),
Manila. He established the Thomasian Angiosperm Phylogeny and Barcoding Group (TAPBG) in the UST Research Center for the Natural and Applied Sciences.
Author contributions: AORD—contributed to the field collections, data analysis, discussion of results, and conclusion of the manuscript. GJDA—led the discussion, editing, and paper review for the manuscript.
Acknowledgements: The authors thank the University of Santo Tomas Herbarium (USTH) for the assistance with species authentication, DENR Region V for granting the gratuitous permits, Roque Laboratory of the UST Graduate School, and Analytical Services Laboratory of the Research Center for the Natural and Applied Sciences (RCNAS), UST. Rene Manzanades and Erroll Monteriola of DENR Region V for providing the map. The first author acknowledges the Commission on Higher Education (CHED) and Bicol University, Legazpi City, for the scholarship grant.
Abstract: Annonaceae is one of the most
prominent families with diverse pollen morphology. The present study aimed to
investigate and describe the pollen morphology of 12 species of Annonaceae from the Bicol Region, Philippines. The pollen
grains were subjected to acetolysis and described
using a scanning electron microscope, and the hierarchical cluster analysis was
done to cluster the pollen grains with similar characters. The 12 Annonaceae species share characters such as monads,
inaperturate, and isopolarity, but they formed three
distinct clusters based on pollen size. Their polar axis (PA) and equatorial
diameter (ED) are statistically significant due to their variability, with PA
ranging 36.41±15.86 µm and ED 28.27±14.27 µm. The polar length-to-equatorial
diameter (PA/ED) ratio is 1.32, with mostly sub-prolate shape. Exine ornamentations showed significant variability among
the 12 Annonaceae species with echinate, rugulate, scabrate, psilate, and verrucate. The pollen morphology of the two
endemic species, namely Friesodielsia
lanceolata (Merr.) Steenis and Goniothalamus
elmeri Merr. is first
reported here. Collections of more endemic Philippine Annonaceae
species are deemed necessary to comprehensively analyze their pollen
characters, which are helpful for infrageneric relationships within the
family.
Keywords: Acetolysis, endemic species,
equatorial diameter, exine ornamentation, palynology,
polar axis, pollen size, pollen shape, pollination, SEM.
Introduction
Annonaceae is a pantropical family comprising 110 genera
and approximately 2,500 species (Chatrou et al. 2012;
Xue et al. 2021). The family members are
characterized by exstipulate, distichous leaves, trimerous perianth of two
whorls of petals, numerous stamens, and free carpels (van Heusden
1992; Chatrou et al. 2012; Couvreur
et al. 2012). Moreover, the family has the greatest basal angiosperm diversity
at both macromorphological and pollen morphological levels (Doyle & Le Thomas 2012). Annonaceae
provide forest and ecosystem services, such as provisioning, regulating,
cultural, and supporting services (Handayani & Yuzammi 2021; Erkens et al. 2023).
They are widely distributed in Asia-Pacific regions such as Thailand, Malaysia,
Borneo, and the Philippines (Turner 2011; Johnson et al. 2021).
The palynology of Annonaceae
has gained interest because it is a significant source of evidence for
systematics and phylogenetic analysis (Doyle & Le
Thomas 1997; Xue et al. 2011; Ragho
2020). The minute pollen grains contain a remarkable degree of
information in their highly resistant sporopollenin wall (Davey et al. 2015),
which provides additional plant identification and classification characters to
solve differences in problematic groups (Okechukwu et
al. 2021); solve complicated taxonomic interrelationships (Saunders et al.
2018).
Several studies on pollen morphology, such as Neo-uvaria Airy Shaw, showed inaperturate, monads with scabrate or micro-echinate exine
ornamentations (Chaowasku et al. 2011); the pollen
grains of some Thai Artabotrys R.Br. were
described as monad pollen, inaperturate, apolar, and
medium to large grains. The pollen shapes were divided into two groups, subprolate & euprolate, and
different exine ornamentations with rugulate & perforate-fossulate
exine sculptures (Eiadhong
& Insura 2014); species from China have small,
medium-sized, and large to very large pollen grains, elliptic, subspherical in monads for Artabotrys,
Fissistigma (Merr.) Steenis, Miliusa Lesch. ex A.DC., Trivalvaria
(Miq.) Miq., Uvaria L., and Polyalthia
Blume, and tetrads for Annona L., Goniothalamus
Hook.f. & Thomson, Mitrephora
Hook.f. & Thomson, and Polyalthia
rumphii (Blume ex Hensch.)
Chaowasku (Gan et al. 2015); three species of Annona
L. have been studied, namely Annona squamosa L. and Annona
senegalensis L. were tetragonal with a globose shape, rugulate exine ornamentation,
inner structure, and Annona muricata L. was
rhomboidal with an ellipsoidal shape, reticulate exine
ornamentation (Okechukwu et al. 2021). The pollen
morphology studies reaffirm the great diversity among and within genera in Annonaceae (Shao & Xu 2017).
While pollen morphology of Annonaceae
species from America and Africa has been studied well (Couvreur
et al. 2008; Turner 2011; Azeez & Folorunso 2014;
Shao & Xu 2018), research in the Philippines remains limited. The
Philippines has 33 genera and 147 species recognized, and 97 are endemic (Pelser et al. 2011 onwards). For the diversity of Annonaceae species, floral inventories and collections are
deemed necessary to study their pollen morphology, which would supplement the
identification and classification of the Annonaceae.
Pollen studies of the Philippine Annonaceae need to
be investigated well, especially among the endemic species. The present study
was the first attempt to study pollen morphology on the 12 species of Annonaceae collected from the Bicol Region, Philippines,
utilizing a scanning electron microscope (SEM); thus, it is important to
provide detailed descriptions and present a better understanding of pollen
diversity.
Materials and Methods
Plant collection
The flowers of Annonaceae
were collected during the explorational surveys for Annonaceae
in the four protected areas (PAs) in the Bicol Region, Philippines, during the
flowering month of July in 2019 and 2021. The PAs include Abasig-Matogdon-Mananap
Natural Biotic Area (AMMNBA) covering Mt. Mananap in
San Vicente, Mt. Matogdon in San Lorenzo Ruiz, and Labo, Camarines Norte; Bulusan Volcano Natural Park (BVNP), Sorsogon; Mt. Isarog Natural Park (MINP) in Panicuason,
Naga City, Camarines Sur, and Mt. Mayon
Volcano Natural Park (MMVNP) in Barangay Mayon, Albay
(Image 1). Gratuitous Permits were secured from the Department of
Environment and Natural Resources (DENR) Region V.
SEM preparation of pollen grains
The flowers of the Annonaceae
species collected from the Bicol Region (Dioneda
& Alejandro 2022, 2023) and pollen grains were placed in microtubes with
labels and stored in the refrigerator at 50 oC.
The present study used the acetolyzation procedure by
Halbritter et al. (2018a). The pollen grains were
placed in a small test tube with a mixture of nine parts acetic anhydride and
one part concentrated sulfuric acid and heated for four minutes at 100 oC. The acetolyzed
mixtures were placed in a water bath while heating. After heating, the liquid
was decanted, and the residues were washed with acetic acid three times. Then, more
water was added to wash further. The mixture was filtered, and the pollen
grains were air-dried. The air-dried pollens were placed on the stub with
carbon tape and inside the SEM chamber (HITACHI TM 3000). For each species, 20
pollen grains were measured, and intricate images of pollen were observed using
the higher resolution of SEM (2000–3000 magnification or more). The SEM
observation was held at the Analytical Services Laboratory, Research Center for
the Natural and Applied Sciences (RCNAS), University of Santo Tomas, España, Manila. Photomicrographs of the examined pollen
grains were taken for further identification.
Pollen descriptions and measurements
The pollen characters used to describe the
pollen grains were pollen shapes, sizes, exine sculpture
or ornamentations, distribution, and apertures (El-Amier
2015; Halbritter et al. 2018b). Punt et al. (2007)
and Halbritter et al. (2018c) were used for pollen
descriptions and terminology. Pollen shape and size terminology followed Erdtman (1952).
The polar axis (PA) and equatorial diameter
(ED) were measured. The equatorial measurement of the pollen grains was done by
measuring the grain from one side of the equator to the opposite side. Polar
measurement was done by measuring one pole to the other to indicate pollen
shape accurately. The mean value of both axes was computed. The shape of the
pollen was determined by the ratio of PA/ED (Table 1). The PA and ED were
subjected to statistical analysis using IBM SPSS software v. 3, and
Hierarchical cluster analysis was used to cluster Annonaceae
species with similar characters and generate the dendrogram to visually
represent the relationships between characters.
Results and Discussion
General description of pollen grains of Annonaceae species from the Bicol Region
The pollen morphology of Annonaceae
from the Bicol Region was notably varied. Mostly, the pollen grains were
monads, a few were dyads, and tetrads. The pollen sizes ranged from small
(10–30 µm), medium-sized (30–50 µm), and large to very large (50–100 µm). The
polar axis (PA) value ranges 36.86 ± 15.86 µm, and the equatorial diameter (ED)
value ranges 28.27 ± 14.27 µm. The total mean value of the polar axis is 35.27
µm, the total mean value of the equatorial axis is 27.22 µm, and the total mean
PA/ED ratio is 1.32, with a generally sub-prolate shape. The exine ornamentations also varied in echinate, rugulate, scabrate, psilate with
micro-perforations, and verrucate. Detailed
morphometry is presented in Tables 2 & 3.
Species-level pollen descriptions
Tribe Miliuseae
Meiogyne cylindrocarpa (Burck) Heusden, 1994 (Image 2)
Pollen unit: monad, pollen size: small to
medium-sized (20–30 µm), polarity: isopolar, pollen
shape: sub-prolate, aperture: inaperturate, PA mean value: 30.94 ± 4.20 µm with
ED mean value 25.37±3.38 µm, PA/ED ratio: 1.22, ornamentation: rugulate.
Monoon grandifolium (Elmer) B.Xue
& R.M.K.Saunders, 2012 (Images 2 & 3)
Pollen unit: monad, small to medium-sized
(20–30 µm), polarity: isopolar, pollen shape:
sub-prolate, aperture: inaperturate, PA mean value 35.47 ± 9.33 µm, ED mean
value 28.27 ± 6.73 µm, PA/ED ratio 1.32, ornamentation: granular-rugulate.
Phaeanthus ophthalmicus (Roxb. ex G.Don) J. Sinclair, 1955 (Images
2&3)
Pollen unit: monad, pollen size: small to
medium-sized (20–30 µm), polarity: isopolar, pollen
shape: prolate, aperture: inaperturate, PA mean value 34.71 ± 8.57 µm, ED mean
value 24.64 ± 5.43 µm, PA/ED ratio 1.41, ornamentation: scabrate.
Polyalthia obliqua Hook.f. & Thomson, 1855 (Images 2&3)
Pollen unit: monad, pollen size: small to
medium-sized (20–30 µm), polarity: isopolar, pollen
shape: prolate, aperture: inaperturate, PA mean value 27.46±5.92 µm, ED mean
value: 20.41±6.11 µm, PA/ED ratio 1.39, ornamentation: verrucate.
Popowia pisocarpa (Blume) Endl. ex. Walp., 1842 (Image 2)
Pollen unit: monad, pollen size: small to
medium-sized (20–30 µm), polarity: isopolar, pollen
shape: sub-prolate, PA mean value 31.85 ± 10.58 µm, ED mean value 27.17 ± 12.41
µm, PA/ED ratio 1.17, ornamentation: scabrate.
Tribe Uvarieae
Fissistigma latifolium (Dunal) Merr., 1919 (Image 2)
Pollen unit: monad, pollen size: small to
medium-sized (10–30 µm), polarity: isopolar, pollen
shape: prolate; aperture: inaperturate, PA mean value 24.47±5.39 µm, ED mean
value 18.15 ± 5.10 µm, PA/ED ratio 1.35, ornamentation: verrucate.
Friesodielsia lanceolata (Merr.) Steenis, 1964 (Image 2)
Pollen unit: monad, pollen size: small to
medium-sized (20–30 µm), polarity: isopolar, pollen
shape: prolate, aperture: inaperturate, PA mean value 33.55±7.70 µm, ED mean
value 24.10 ± 7.82 µm, PA/ED ratio 1.39, ornamentation: echinate.
Uvaria monticola Miq., 1865 (Images 2
& 3)
Pollen unit: monad, pollen size: medium to
large (30–50 µm), polarity: isopolar, pollen shape:
prolate, aperture: inaperturate, PA mean value 32.20 ± 2.46 µm, ED mean value
28.81 ± 2.51 µm, PA/ED mean value 1.12, ornamentation: coarsely rugulate.
Tribe Canangeae
Cananga odorata (Lam.) Hook.f. &
Thomson, 1855 (Images 2)
Pollen unit: dyad, pollen size: large to very
large-sized (50–100 µm), polarity: isopolar, pollen
shape: sub-prolate, apertures: inaperturate; PA value 73.14 ± 14.91 µm, ED mean
value 61.05 ± 15.75 µm, PA/ED ratio 1.20, ornamentation: psilate with microperforations.
Drepananthus acuminatus (C.B.Rob.)
Survesw. & R.M.K. Saunders, 2010 (Image 2)
Pollen unit: monad, pollen size: small to
medium-sized (20–30 µm), polarity: isopolar, pollen
shape: prolate, aperture: aperturate; PA mean value
29.40±8.72 µm, ED mean value 19.31±6.27 µm, P/E ratio 1.52, ornamentation: scabrate
Tribe Annoneae
Goniothalamus elmeri Merr., 1912 (Image
2)
Pollen unit: tetrad, pollen size: small to
medium-sized (20–100 µm), polarity: isopolar, pollen
shape: prolate, aperture: inaperturate, PA mean value 33.62 ± 10.95 µm, ED mean
value 24.28 ± 7.51 µm, PA/ED ratio 1.38, ornamentation: coarsely rugulate.
Tribe Xylopieae
Artabotrys suaveolens (Blume) Blume, 1830 (Image 2)
Pollen unit: monad, size (pollen unit): small
to medium-sized (20–30 µm), polarity: isopolar,
pollen shape: prolate, apertures: inaperturate; PA mean value 34.71 ± 8.57 µm,
ED mean value 23.43 ± 8.27 µm, PA/ED ratio 1.48, ornamentations rugulate.
Discussion
The pollen morphology of basal angiosperms like
the Annonaceae is highly diverse (Lu et al. 2015).
This diversity of pollen types gained interest because it provides insights
into the evolutionary history. Annonaceae, one
of the most prominent primitive families, produces a variety of pollen types,
including monads, dyads, tetrads, and polyads composed of eight, 16, or 32
grains (Walker 1971). The variety of pollen grains in Annonaceae
in terms of size, aperture number, shape, and exine
ornamentations was observed in many studies (Eiadthong
& Insura 2014; Shao & Xu 2018). According to
Lora et al. (2014), pollen production in monads is plesiomorphic in
angiosperms, but the aggregation into tetrads has arisen independently at
different times during the evolution of flowering plants. Aggregated forms
offer advantages in situations involving infrequent pollinators, short pollen
viability, pollen transfer periods, and protection from desiccation.
Furthermore, aggregated pollen is considered an advanced character in Annonaceae, surpassing the traditional monad form (Azeez
& Folorunso 2014).
The 12 species of Annonaceae
have shared pollen characteristics like single pollen grains, monads, and
inaperturate pollen, except dyads for Cananga
odorata and tetrad for Goniothalamus
elmeri. The present study confirms that the genus
Cananga is often observed as a
dyad; although some authors reported that some pollen grains of Cananga were possibly in tetrads, the links between
pollen pairs might have been loose within the tetrad and resulted in dyad
pollen grains (Walker 1971; Xu & de Craene 2012;
Li et al. 2023). On the other hand, pollen grains of Goniothalamus
elmeri were tetrahedral tetrads, and different
types were seen as tetragonal in G. sawtehii C.E.C.Fisch, G. tamirensis Pierre ex Finet
& Gagnep., and G. undulatus
Ridl. at the same time, G. wynadensis
(Bedd.) Bedd. has two types
of decussate and tetragonal tetrads (Jayan & Sreekala 2023).
In terms of the hierarchical cluster analysis,
the pollen grains from the Bicol Region formed three clusters (Figure 1). The
species Cananga odorata
belongs to cluster I; it has dyad pollen grains, with the most significant
variation in the PA and ED, pollen size of 50–100 µm, and psilate with
micro-perforation exine ornamentations. In cluster
II, eight species share characters of pollen grains as monads, with sizes
ranging from small to medium (20–30 µm), namely, Artabotrys
suaveolens (Blume) Blume, Friesodielsia
lanceolata (Merr.) Steenis, Goniothalamus elmeri Merr., Phaeanthus ophthalmicus
(Roxb. ex G.Don)
J. Sinclair, Meiogyne cylindrocarpa
(Burck) Heusden, Monoon grandifolium
(Elmer) B.Xue & R.M.K.Saunders,
Popowia pisocarpa
(Blume) Endl. Ex Walp., and
Uvaria monticola
Miq. The species Goniothalamus
elmeri was found nearer the cluster’s centre with prolate shapes, while the Uvaria
monticola was found farther from the cluster centre with prolate-spheroidal shapes. On the other hand,
in cluster III, three species, namely Drepananthus
acuminatus (C.B.Rob.) Survesw. & R.M.K.Saunders, Fissistigma latifolium
(Dunal) Merr., and Polyalthia obliqua Hook.f. & Thomson shares pollen characters of monads,
inaperturate, and prolate, but differs in the sizes of the PA, ED, and exine ornamentations.
Pollen sizes greatly vary among the species,
from small to very large grains. The PA and ED are statistically significant
due to a wide range of variability (Table 2). The species Fissistigma
latifolium has smaller pollen sizes from small to
medium (10–20 µm) and medium to large (30–50 µm) in Uvaria
monticola and Cananga
odorata, while very large as tetrahedral-type
tetrad (100 µm) but as monads (20 µm) for Goniothalamus
elmeri. The variability in pollen size of Annonaceae is highly homoplastic and influenced by the
preparation method, which appears to be shrunken using SEM rather than in the
light microscope (Halbritter et al. 2018b). Although
grain size seems unstable, it plays a role in the systematics (Lee 1984).
According to Ejsmond et al. (2011), the desiccation
intensity of pollen grains may decrease the pollen sizes due to climatic
factors such as temperature, potential evapotranspiration, and altitude, which
may significantly affect pollen grains’ sizes. Environmental stresses like
heat, drought, cold, and humidity affect pollen production & viability.
During anthesis, the pollen grains of some plants enter a metabolically
“inactive state” to support survival during pollen dispersal. The pollen grains
lose water and reach a state of complete or partial desiccation tolerance,
depending on environmental conditions (Pacini & Dolferus 2019). Furthermore, pollen size is also affected
by the mineral content of the soil, shoot defoliation, and climate change.
Higher concentrations of soil nitrogen and phosphorus have been reported to
increase pollen grains’ size, yield, and germinability (Lau & Stephenson
1994).
The prominent pollen shapes were prolate,
sub-prolate, and prolate-spheroidal (Table 3). The prolate shape (1.34–1.99)
was observed in the six species, namely Artabotrys
suaveolens, Drepananthus
acuminatus, Fissistigma
latifolium, Friesodielsia
lanceolata, Goniothalamus
elmeri, Phaeanthus
ophthalmicus, and Polyalthia
obliqua, while sub-prolate shape (1.15–1.33) was
observed in Cananga odorata,
Meiogyne cylindrocarpa,
Monoon grandifolium,
Popowia pisocarpa,
and prolate-spheroidal shape (1.01–1.14) was found only in Uvaria
monticola. Friesodielsia
desmoides (Craib) Steenis has spheroidal shape compared to F. lanceolata with prolate, and Artabotrys
hexapetalus (L.f.)
Bhandari has perprolate shape compared to Artabotrys suaveolens
with a prolate shape. The PA/ED ratio was not statistically significant because
it showed no variability among the species. Moreover, most of the 12 pollen
grains are isopolar, with identical proximal and
distal poles. Most species are inaperturate with no visible aperture or
indication of a pole, except for Drepananthus
acuminatus, which has a small opening (Image 2).
This small opening is a disulcate aperture,
as confirmed by Xu & de Craene
(2012). Hence, pollen aperture is a significant criterion for identifying
and describing pollen (Waha & Merawetz
1988). Nevertheless, recognizing apertures’ position, shape, and nature is
often problematic. The pollen grain is surrounded by a resistant wall called exine; certain regions of the pollen surface receive little
or no exine deposition, leaving an aperture that
serves as a site for pollen tube exit (Sarwar & Takahashi 2012; Zhang et
al. 2017).
The pollen wall structure, exine,
is one of the characteristics used for identification (Sari et al. 2015). Rugulate ornamentation was observed in the pollen grains of
Artabotrys suaveolens,
Goniothalamus elmeri, Meiogyne cylindrocarpa,
Monoon grandifolium,
and Uvaria monticola.
The scabrate ornamentations were seen in Phaeanthus ophthalmicus,
Popowia pisocarpa, and Drepananthus acuminatus. In
addition, verrucate was observed in Polyalthia obliqua and Fissistigma latifolium, and
the psilate with micro-perforation was found only in Cananga odorata. In the study
of Shao & Xu (2017), Goniothalamus laoticus (Finet & Gagnap.) Bân has psilate
ornamentations and Polyalthia bullata King rugulate with
different exine ornamentations; Artabotrys
hexapetalus has microrugulate
and coarsely rugulate in Fissistigma
oldhamii (Hemsl.) Merr. exine ornamentations (Xu
& de Craene (2012) (Table 4). The above results
corroborate the diverse exine ornamentations in Annonaceae species. Some studies also reaffirm the variety
of exine ornamentations in some species such as the
Asian genus of Friesodielsia which were
heterogeneous (Walker 1971) with echinate-perforate with well-developed spines
but differs from the African genus with coarsely verrucate
pollen ornamentations, Uvaria with coarsely rugulate observed in Uvaria
grandiflora (Lesch. Ex DC) and scabrate in Uvaria
macrocarpa (Dunal)Vahl (Xu & de Craene 2012)
and some species in the tribe Xylopieae with coarsely
fossulate-perforate ornamentations (Shao & Xu
2017). Despite the differences among species, exine
ornamentation patterns are one of the important characteristics of pollen,
which is significant in the study of genetic evolution and systematic taxonomy.
The ornamentation exine of pollen grains is highly
conserved and genetically stable (Xu & de Craene
2012; Shao & Xu 2017).
Interestingly, the surface ornamentation of
pollen grains correlates with pollination types by interacting with pollinators
and how the pollen can efficiently be transferred from one flower to another (Sannier et al. 2009). The pollen ornamentation, such as
spines and rough surfaces, can make pollen more sticky
and less likely to fall off on the pollinator’s body, allowing it to better
adhere to the pollinators like insects or animals, increasing the number of
flowers it can reach (Hasegawa et al. 2021). The identified exine
ornamentations with complex patterns in the present study include some pollen
grains with echinate, rugulate, scabrate,
and verrucate ornamentations, indicating that animals
have been pollinating flowers of Annonaceae. The
plants pollinated by animals develop complex patterns with various decorations
on their pollen surface. The various spines, ridges, and papilla on their exine surface may help pollen grains attach to animal
pollinators, influencing how pollen grains are dispersed and interact with the
pollinators. This finding corroborates that the majority of pollinators of the
family Annonaceae are beetles included in the family
of Nitidulidae, Staphylinidae,
Chrysomelidae, and Curculionidae
and other insect groups like thrips, flies, bees, and
cockroaches have also been identified as pollinators in some Annonaceae species such as Popowia
pisocarpa and Xylopia
aromatica (Lam.) Mart. (Gottsberger
1999; Momose et al. 2006; Lau et al. 2016).
Furthermore, the exine
ornamentations can deter pollen consumption by flower visitors than the target
pollinators (Lynn et al. 2020). In addition, the exine
ornamentations facilitate the pollen-stigma interaction, pollen hydration, and
release of pollen tubes for fertilization (Mach 2012). In contrast, the psilate
with micro-perforations in Cananga odorata indicates that it was pollinated by wind or
water, and a smooth surface may improve the aerodynamics of pollen. Hence,
water is not a common method of pollination in Annonaceae
(Lau et al. 2016).
Two endemic species were included in the
study, namely, Friesodielsia lanceolata and Goniothalamus
elmeri, and they were compared with the study of
Xu & de Craene (2012) and Shao & Xu (2017)
(Table 4). The species Friesodielsia lanceolata pollen grains are prolate monads, echinate,
PA of 35.55 µm, and differ from F. desmoides
pollen grains are spheroidal monads with no visible aperture, and
echinate-perforate with well-developed spines and a mean PA of 29 µm, while Goniothalamus elmeri shares
characteristics with G. laoticus of
tetrahedral tetrad pollen, inaperturate and PA of ±100; however, they differ in
exine ornamentations of rugulate
and psilate, respectively. Although these species have the same genus, pollen
sizes, shapes, and exine ornamentations differ.
Conclusion
The pollen morphology of the 12 Annonaceae studied exhibited high diversity, and they
shared characters such as monad, inaperturate, and isopolar
characters, but formed three clusters based on pollen size. Most have
sub-prolate pollen shapes. They varied significantly in PA & ED axis and
size from small to very large, and exine
ornamentations include echinate, rugulate, psilate
with micro-perforations, scabrate, and verrucate. The present study was the first attempt to
investigate 12 species of Annonaceae collected from
the Bicol Region, Philippines. Pollen morphology of two endemic species is
first reported here. Therefore, increasing the collection of endemic Philippine Annonaceae is
recommended to search for new pollen characters that generate a comprehensive
analysis of infrageneric relationships and family classifications.
Table 1. Pollen shape classes and suggested relationships
between polar axis (PA) and equatorial diameter (ED) (Erdtman
1952).
|
Pollen shape classes |
PA / ED |
100 x PA / ED |
|
Peroblate |
<4/8 |
< 50 |
|
Oblate |
4/–6/8 |
50–75 |
|
Suboblate |
6/8–7/8 |
75–88 |
|
Oblate spheroidal |
7/8–8/8 |
88–100 |
|
Prolate spheroidal |
8/8–8/7 |
100–114 |
|
Subprolate |
8/7–8/6 |
114–133 |
|
Prolate |
8/6–8/4 |
133–200 |
|
Perprolate |
>8/4 |
>200 |
Table 2. SEM pollen morphometry of the 12 Annonaceae species from the Bicol Region, Philippines (Erdtman 1952).
|
Name of species |
PA value |
ED value |
PA/ED ratio |
|
Tribe Miliusae |
|
|
|
|
Meiogyne cylindrocarpa (Burck) Heusden |
30.94 ± 4.20 |
25.37 ± 3.38 |
1.22 |
|
Monoon grandifolium (Elmer) B.Xue &
R.M.K.Saunders |
35.47 ± 9.33* |
26.84 ± 6.73* |
1.32 |
|
Phaeanthus ophthalmicus (Roxb. ex G.Don) J.Sinclair |
34.71 ± 8.57* |
24.64 ± 5.43* |
1.41 |
|
Polyalthia obliqua Hook.f. & Thomson |
27.46 ± 5.92 |
20.40 ± 6.11 |
1.35 |
|
Popowia pisocarpa (Blume) Endl. ex. Walp. |
31.85 ± 10.58* |
27.17 ± 12.41* |
1.17 |
|
Tribe Uvarieae |
|
|
|
|
Fissistigma latifolium (Dunal) Merr. |
24.47 ± 5.33 |
18.15 ± 5.10 |
1.35 |
|
Friesodielsia lanceolata (Merr.) Steenis |
35.55 ± 7.70 |
24.1 ± 7.82 |
1.39 |
|
Uvaria monticola Miq. |
32.20 ± 2.46 |
28.81 ± 2.51 |
1.12 |
|
Tribe Canangeae |
|
|
|
|
Cananga odorata (Lam.) Hook.f. & Thomson |
73.14 ± 14.91* |
61.05 ± 15.75* |
1.20 |
|
Drepananthus acuminatus (C.B.Rob.) Survesw & R.M.K.Saunders |
29.40 ± 8.72* |
19.31 ± 6.27* |
1.52 |
|
Tribe Annoneae |
|
|
|
|
Goniothalamus elmeri Merr. |
33.62 ± 10.95* |
24.28 ± 7.51* |
1.38 |
|
Tribe Xylopiaeae |
|
|
|
|
Artabotrys suaveolens (Blume) Blume |
34.71 ± 8.57* |
23.43 ± 8.27* |
1.48 |
|
Mean values |
36.41 ± 15.86* |
28.27 ± 14.27* |
1.32** |
*—significant | **—not significant.
Table 3. Pollen morphology of the 12 species of Annonaceae pollen grains from Bicol Region, Philippines
(Punt et al. 2007; Halbritter et al. 2018b).
|
Name of species |
Pollen size (µm) |
Pollen size |
Pollen shape |
Pollen unit |
Pollen
aperture |
Exine ornamen-tation |
|
Tribe Miliusae |
|
|
|
|
|
|
|
Meiogyne cylindrocarpa (Burck) Heusden |
20–30 |
Small–medium |
Sub-prolate |
Monad |
Inaperturate |
Rugulate |
|
Monoon grandifolium (Elmer) B.Xue &
R.M.K.Saunders |
20–30 |
Small–medium |
Sub-prolate |
Monad |
Inaperturate |
Rugulate |
|
Phaeanthus ophthalmicus (Roxb. ex G.Don) J. Sinclair |
20–30 |
Small–medium |
Prolate |
Monad |
Inaperturate |
Scabrate |
|
Polyalthia obliqua Hook.f. & Thomson |
20–30 |
Small–medium |
Prolate |
Monad |
Inaperturate |
Verrucate |
|
Popowia pisocarpa (Blume) Endl. ex. Walp |
20–30 |
Small–medium |
Sub-Prolate |
Monad |
Inaperturate |
Scabrate |
|
Tribe Uvarieae |
|
|
|
|
|
|
|
Fissistigma latifolium (Dunal) Merr. |
10–30 |
Small–medium |
Prolate |
Monad |
Inaperturate |
Verrucate |
|
Friesodielsia lanceolata (Merr.) Steenis |
20–30 |
Small–medium |
Prolate |
Monad |
Inaperturate |
Echinate |
|
Uvaria monticola Miq. |
30–50 |
Medium–large |
Prolate-Spheroidal |
Monad |
Inaperturate |
Rugulate |
|
Tribe Canangeae |
|
|
|
|
|
|
|
Cananga odorata (Lam.) Hook.f. & Thomson |
50–100 |
Medium–very large |
Sub-Prolate |
Dyad |
Aperturate |
Psilate-microper-foration |
|
Drepananthus acuminatus (C.B. Rob.) Survesw & R.M.K.Saunders |
20–30 |
Small–medium |
Prolate |
Monad |
Aperturate |
Scabrate |
|
Tribe Annoneae |
|
|
|
|
|
|
|
Goniothalamus elmeri Merr. |
20–100 |
Medium–very large |
Prolate |
Tetrad |
Inaperturate |
Rugulate |
|
Tribe Xylopiaeae |
|
|
|
|
|
|
|
Artabotrys suaveolens (Blume) Blume |
20–30 |
Small–medium |
Prolate |
Monad |
Inaperturate |
Rugulate |
Table 4. Comparison of pollen characters of pollen grains
from Bicol Region, Philippines with the pollen grains from Thailand (Xu &
de Craene 2012; Shao & Xu 2017).
|
Pollen types |
Friesodielsia lanceolata* |
Friesodielsia desmoides |
Goniothalamus elmeri* |
Goniothalamus laoticus |
Polyalthia obliqua* |
Polyalthia bullata |
Artabotrys suaveolens* |
Artabotrys hexapetalus |
Fissistigma latifolium* |
Fissistigma oldhamii |
|
Pollen unit |
monad |
monad |
tetrad |
tetrad |
monad |
monad |
monad |
Monad with single furrow |
monad |
Monad |
|
Pollen shape |
prolate |
spheroidal |
Tetrahedral |
tetrahedral |
prolate |
prolate |
prolate |
Perprolate |
prolate |
Prolate spheroidal |
|
Pollen aperture |
Inaperturate |
Inaperturate |
inaperturate |
Inaperturate |
Inaperturate |
inaperturate |
Inaperturate |
Inaperture |
Inaperturate |
inaperturate |
|
Pollen ornamentation |
Microechinate |
Echinate-perforate with spines |
rugulate |
psilate |
verrucate |
rugulate |
rugulate |
Microrugulate |
verrucate |
Coarsely rugulate |
|
Polar axis (µn) |
35.55 |
29 |
100 |
105 |
27.46 |
48 |
34.71 |
56 |
24.47 |
35 |
Legend: * present study
For
figure & images - - click here for full PDF
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