Pollen Morphological Description of Some Plants

A: POLLEN MORPHOLOGY OF CERTAIN TROPICAL ANGIOSPERMOUS PLANTS

Tropical angiospermous flora of India, very rich in families, genera and species is highly diversified. Similarly the pollen morphology of these plants shows great variation. It is not possible to describe pollen morphology of many of these plants in this volume. However, the Mimosaceae (Mimosoids) family is chosen for a detailed pollen morphological description for two reasons. The plants belonging to this family are cultivated widely and some of them grow naturally and abundantly in different regions of India and other tropical areas. From the student's point of view the pollen material for detailed pollen morphological study is easily accessible. The pollen of this family vary from monads to polyads. There is tremendous variation in the pollen morphology of these plants. Significant contribution on this theme has been recently made by Cheriyan Panicker (2002).

It is appropriate to mention here that detailed pollen morphology of several plants is discussed in the chapters on aerobiology as these pollen have great relevance to allergic manifestations. However, pollen illustrations of some tropical angiospermous plants, particularly abundant in the Western Ghats have been incorporated in this chapter (Figs. 5.1 a-p).

Pollen Morphology of Mimosoids

The following pollen morphological descriptions of some mimosoids are accompanied by Fig. 5.2 a-r

Acacia auriculiformis A. cunn.

It is commonly known as Australian Acacia or golden shower plant. In India the plant was introduced from tropical Australia. The trees without spines grow up to 10-15 m high. The branchlets are glabrous and phyllodes are elliptic, falcate, thick coriaceous, glabrous and palminerved. The trees produce drooping spikes of golden yellow flowers. Stamens are numerous

a. Anona squamosa, Anonaceae -pollen grains are in Dyads with foveolate - striate sculpturing.

c. Gloriosa superba - Liliaceae -pollen exine showing reticulate sculpturing.

e. Dendocalamus strictum, Poaceae -pollen showing single pore and psilate sculpturing.

Pollen Grain Exine And Intine

b. Glosiosa superba - Liliceae -Peroblate monocolpate pollen.

Echinate Pollen

d. Dendocalamus strictus - Poaceae - pollen spherical, monoporate, oblate spheroidal spherical, monoporate, costate.

Pollen Grain Crinum

f. Crinum pretense, Amaryllidaceae pollen grain subprolate, dizonocolpate, exine sculpturing echinate.

Hibiscus Flower Enlarged Outline

g. Crinum pretense, Amaryllidaceae trizonosyncolpate pollen with echinate sculpturing.

Malvaceae Pollen

h. Urena lobota - Malvaceae - pantoporate pollen with circular to oblate pori, echinate sculpturing, echinae lanceolate in outline, tips obtuse.

Malvaceae Pollen

i. Hibiscus hirtus - Malvaceae - pollen oblate spheroidal, pantoporate, exine with echinate sculpturing, with convex bulbous protuberances.

Morphology Pollen Grains
k. Hibiscus lobatus - Malvaceae -pantoporate pollen with circular to oblate pori, echinate sculpturing, echinae lanceolate in outline, tips obtuse.

j. Abutilon indicum, Malvaceae -pollen oblate spheroidal, trizonocolporate, colpi very faint, narrowly elliptic. Exine with echinate sculpturing, echinae with acute tips and swollen bases.

Echinate Pollen

l. Cereus dayamii - Cactaceae Pollen oblate spheroidal, trizonocolpate, with echinate sculpturing.

m. Xanthium strumarium - Asteraceae -enlarged view of exine sculpturing.

n. Xanthium strumarium Asteraceae - pollen grain suboblate, trizonocolporate, Exine 4.25 pm thick, sculpturing scabrate or microechinate, echinae situated on polygonal cushion bases.

Cucurbita Pollen

o. Citrullus lanatus - Cucurbitaceae -prolate pollen, trizonocolporate, exine with reticulate sculpturing, lumina irregularly polygonal, with margo.

n. Xanthium strumarium Asteraceae - pollen grain suboblate, trizonocolporate, Exine 4.25 pm thick, sculpturing scabrate or microechinate, echinae situated on polygonal cushion bases.

o. Citrullus lanatus - Cucurbitaceae -prolate pollen, trizonocolporate, exine with reticulate sculpturing, lumina irregularly polygonal, with margo.

Cissampelos pareira, Menispermaceae -Pollen prolate spheroidal, polar outline triangular, trizonocolporate, colpi narrowly elliptic, operculate. Exine with reticulate sculpturing, lumina irregularly trigonal to variously polygonal.

Fig. 5.1a-p Pollen morphology of tropical angiospermous plants, particularly abundant in the Western Ghats, India.

with 3-3.5 mm long filaments, which are basaly united. The flowering period is from July to February. The mode of pollination is amphiphilous.

It is the second largest pollen producer in the family Mimosaceae. About 120 anthers are produced per flower. The catkin bears 115 flowers with 120 anthers producing 8 polyads containing 16 pollen. Thus, about 128 pollen grains are produced per anther and 15,360 per flower and 17,66,400 per inflorescence.

The pollen grains in this plant are clustered in spherical polyads with 16 grains in each, arranged in a regular pattern that is 8 grains in the centre arranged four in two layers each, one layer directly above the other which are surrounded in turn by 8 peripheral grains. Apertural condition in individual pollen grains is characterized by three pores, which are not so well defined. SEM of these grains shows exine surface with the central square shaped depressions bounded by raised undulate margins. These depressions and margins have low pock-mark depressions (Figs. 5.2 a, b).

The pollen grain is squarish with a reticulate exine surface, packed close to each other like bricks. Polyads vary in diameter from 41.2 to 45.3 ^m, whereas the size of individual pollen grains varies from 8-11 mm across.

Acacia dealbata link

Commonly called Silver wattle, consists of unarmed trees 12-15 m in height, with silvery pubescent branchlets bearing bipinnate leaves, which are grown as avenue trees. The plant is native of Northeast Australia, which was introduced and grown at higher altitudes in the Nilgiris. The tree produces flowers in axillary and terminal panicled globular heads 3-4 mm across. Flowers are minute, scented and yellow in colour. The flowers have numerous stamens with 1-1.5 mm long filaments.

The anthers produce polyads with 16 pollen units adhering to each other. The pollen are identical and tetragonal in shape. Pollen grains are triporate with deep rectangular depressions and clearly defined rounded edges. The exine surface is pockmarked and reticulate. Polyad size ranges from 38.12 to 41.36 mm (Fig. 5.2c).

Adenanthera pavonina

The species is a native of India, Sri Lanka, Thailand and China. The trees of this species are known to grow to 8-12 m in height with glabrous branchlets and two pinnate leaves. Small yellow coloured flowers are produced in axillary raceme, which may be 12-20 cm long. The androecium has 10 stamens with free filaments and gland-crested anthers. 16-celled polyads produced in anthers are spherical. Polyads vary in size from 4143.9 mm and individual pollen grains measure 12.67 to 16.67 mm across. The individual pollen grains in polyad are irregularly arranged. Occasionally polyads get separated into tetrads during acetolysis. The boundary of the grains in polyads is smooth but at its centre, exine materials are deposited regularly giving a rough appearance. The grains are trizonoporate with exine characterized by rugulate sculpturing (Figs. 5.2-d, e).

Albizia falcataria Linn

The plants of this species are natives of Guinea and Solomon isles. They grow up to 15 m high. They bear creamy white flowers in terminal or axillary panicles 15 cm long. The androecium comprises numerous stamens with 1 cm long filaments united to form a 3 mm long staminal tube.

The anther produces 16-celled polyads measuring 66.26 to 70.42 mm in which the grains are arranged in a regular pattern. Individual pollen grains have a cushion like swollen surface without depressions. The central area of the pollen grain wall is marked by distinct rugulate ornamentation, gradually smoothening towards the margins. Pollen grains are 3-zonoporate with sparsely present micropunctae (Figs. 5.2f, g, h).

Polyad PollenPolyad Pollen

Fig. 5.2a & b Acacia auriculiformis a. SEM of polyad showing surface details b. Enlarged SEM view of polyad showing exine ornamentation, major and minor surface depressions.

b. Enlarged SEM view of polyad showing exine ornamentation, major and minor surface depressions.

Polyad Pollen

Fig. 5.2c Acacia dealbata SEM of polyad showing pollen arrangement.

Fig. 5.2d Adenanthera pavonina SEM of polyad showing irregular arrangement of pollen.

Onementation Pollen
Fig. 5.2e Adenanthera pavonina Enlarged SEM view of part of polyad showing the rugulate pattern of exine ornamentation. Broad interspaces of pollen are seen clearly.

Fig. 5.2f,g,h Albizia falcataria (f) LM photomicrograph of polyad.

Fig. 5.2g SEM of polyad showing regular rectangular pollen with cushion like surface.

Description Pollen

Fig. 5.2i Albizia lebback LM of polyad showing a group of four pollen grains separated during acetolysis.

Fig. 5.2h Enlarged SEM of a pollen in polyad showing central rugulate ornamentation, gradually smoothening towards the margins.

Fig. 2.5j,k,l Leucaena leucocephala j. SEM of equatorial view of pollen showing two elongated colpi.
Albizia Pollen

Fig. 5.2k SEM of polar view of pollen Fig. 5.2l SEM showing scrobiculate showing three broad furrows terminating exine pattern.

in rounded ends.

Fig. 5.2k SEM of polar view of pollen Fig. 5.2l SEM showing scrobiculate showing three broad furrows terminating exine pattern.

in rounded ends.

Pollen Tetrad

Fig. 5.2m & n Mimosa invisa var. invisa m. SEM of pollen tetrad.

Description Pollen

Fig. 5.2m & n Mimosa invisa var. invisa m. SEM of pollen tetrad.

Fig. 5.2n Enlarged SEM showing tuberculate exine sculpturing.

Mimosa Pudica Pollen

Fig. 5.2o Mimosa pudica SEM picture of portion of a tetrad showing compound tubercles fused along the lateral ridges.

Fig. 5.2p and q Prosopis juliflora LM photomicrograph of equatorial view showing details of colpus.

Monocolpate Pollen

Fig. 5.2q SEM photomicrograph of pollen grains in equatorial and polar views.

Albizia Pollen
Fig. 5.2r SEM photomicrograph showing enlarged polar view of pollen. Figs. 5.2 a to r Pollen morphology in SEM of some Mimosoids.

Albizia lebback Linn

The plants of this species are natives of India, Sri Lanka, South East Asia and South China. They are usually grown as avenue trees for shade and have scented greenish white flowers. The trees can grow as tall as 20 m. The flowers are in axillary, solitary or 2-3 umbellate heads with numerous stamens, which are monoadelphous with 3 mm long filaments, which are united below to form up to 5 mm long staminal tube.

Pollen grains, which have been clinically proved to be allergenic are clustered in spherical polyads with 16 grains which are tetergonal. Polyads when subjected to acetolysis may separate into pollen tetrads, which measure in 64.2 to 66.3 ^m in diameter. Individual pollen grains are 19 -21 ^m in diameter. The pollen wall consists of exine, which is indistinctly foveolate with low laminar and lowly raised muri. Pollen are three zonoporate without depression (Fig. 5.2i).

Leucaena leucocephala Linn

The plants of this species though natives of South America are widely grown in the tropics. The leaves of these plants are used as fodder for cattle. The plants represent small trees growing to a height of 4-6 m. They produce creamy white flowers in axillary dense globose heads; solitary or in clusters of 2-3, only 10 stamens are produced per flower. The plants flower profusely from July to March.

The pollen grains produced in anthers are monads, their polar view shows them to be spheroidal or triangular. They show tricolpate apertural condition where colpi are broad and taper to rounded ends. Pollen are 3-zonocolporate wtih scrobiculate exine ornamentation (Figs. 5.2j, k and l). Individual scrobicule with punctate lumen are surrounded by a thick annulus. Pollen grains vary from 57.26 to 59.42 mm in length in equatorial view whereas in polar view they range between 39.4 and 42.4 mm in diameter.

Mimosa invisa mart.var.invisa

The plants of this species are natives of South America, but now grow profusely as 'weeds' in India. They are straggling shrubs with an angled stem, pubescent-hirsute and armed with downwardly pointed prickles. Flowers are borne in inflorescence, which is axillary, solitary or paired globose heads 1-1.2 cm in diameter. The flowers are characterized by a minute calyx and corolla with four pink petals united at the base. The androecium consists of eight stamens having 4-5 mm long filaments.

Anthers have pollen tetrads, which are spherical or prolate spheroidal. In the pollen tetrad both tetrahedral and isobilateral pollen arrangements are observed. Exine ornamentation is tuberculate, pores are ill defined (Figs. 5.2m, n). Pollen tetrads are 19.6 to 23.2 ^m and individual pollen grains are 10.2 to 11.2 ^m in diameter.

Mimosa pudica Linn

These spreading herbs with prickly stems are natives of South America but were introduced and naturalized in India. The plant is referred to as a 'sensitive plant' or 'Touch me not' on account of their leaves, which are sensitive to touch when 2-3 pairs of pinnae fold in. Flowers are in axillary heads solitary or in clusters of 2-3, with 2-3 cm long peduncles. Flowers are pink and 0.6 mm across. The calyx tube is 1 mm long and four lobed. Petals are four in number. Stamens are four in number having 6 mm long filaments.

Pollen are produced in tetrads and released to the air in the same condition after dehiscence of the anther. Both tetrahedral and isobilateral arrangements are seen in the tetrads which are 7.6 to 9.2 ^m in diameter, whereas individual pollen grains are 3.9 to 4.5 ^m in diameter. Exine ornamentation is characterized by tubercules. The central area of individual pollen grains is marked by tubercles, merging into the lateral ridges with completely fused tubercles (Fig. 5.2o).

Prosopisjuliflora sw

Though it is native of North and Central America, it is cultivated and grows profusely in semiarid regions of both the northern and southern regions of India and the Middle -East. It is often introduced for afforestation. The armed trees grow up to a height of 8 m. Branchlets are glabrous with 1-1.5 cm long axillary spines. Leaves are bipinnate with 1 - 3 pairs of pinnae. Each pinna bears 15 - 18 pairs of leaflets, which are oblong, inequilateral and obtuse at both ends.

The specific name Juliflora is derived from the Latin word juliflorous meaning blooming with catkins, which are axillary, solitary or in clusters of 2-4 and 8-12 cm long. The creamy flowers in the catkin have campanulate calyx and five white petals, which are joined below to form a tube. Stamens are 10, free having 4-4.5 mm long filaments and glandular anthers.

The pollen grains are in monads. They are spheroidal or triangular in shape, radially symmetrical, subisopolar with 2-zonocolporate aperature. Exine is punctuated, scrobiculate, formed into islands of various sizes and shapes. The valleys between islands have punctuated scrobiculate ornamentation. Colpi have a circular operculum at the region of the ora. Pollen grains range from 23.6 to 27.1 ^m in polar view and 26.6-28.2 ^m in equatorial view (Figs. 5.2p, q, r).

B: POLLEN MORPHOLOGY OF CERTAIN ANGIOSPERMOUS PLANTS FROM TEMPERATE REGIONS

A brief description of a few allergically important plants and their pollen, common in temperate regions has been given below. On the basis of similarity in pollen morphological characters they have been grouped in 5 groups and the same are illustrated in the form of line drawings in Figs. 5.2, 5.3, 5.4, 5.5, 5.6 and 5.7.

In addition, pollen morphology of a few common temperate plants has been described below. These descriptions are supported by photomicrographs in Figs. 5.8, 5.9, 5.10, 5.11, 5.12, 5.13 and 5.14.

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Responses

  • assunta
    Is the pollen morphology of hibiscus lobatus was done?
    3 years ago
  • BERTHA
    What are the description of acacia auriculiformis based on the pollen?
    3 years ago
  • bernd
    What do you mean by pollen grains of Acacia?
    3 years ago
  • hanna hossi
    What is isobilateral arrangement of tetrad?
    3 years ago
  • Ryan Munro
    What is the pollen shape of citrulus lanatus?
    3 years ago
  • Stefanie
    How many calyx, corolla and pollen grains are found in the flower of prosopis juliflora?
    2 years ago
  • Anita Zito
    What are the pollen grain arrangement of albizia sama?
    2 years ago
  • joel
    Do mimosa pudica possess compound pollen grain?
    2 years ago
  • luigia
    Where does pollen grains present in mimosa plant?
    1 year ago

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