ABSTRACT: Morphological characters of pollen of eight (8) species of the Genus Ipomoea found in Akwa Ibom State were examined with an Olympus light microscope. All the pollen grains were radially symmetrical, spherical from prolate-spheroidal to oblate-spheroidal with an apolar (circular) outline, their sculpturing was echinate and they were also polyporate pantoporate. Ipomoea nil (Linn.) Roth had the largest pollen grains (49.70-50.20µm) and had the shortest spines (5.30µm) with the widest spine base (5.30µm) while I. velutipes Welw.ex Rendle had the smallest pollen grains (29.10-30.20µm) but had the longest spines (10.80µm).I. cairica (Linn.) Sweet had a narrow base (3.10µm).The exine was thickest in I. muricata (Linn.) Jacq. (5.00µm) and thinnest in I. intrapilosa Rose and I. involucrata P. Beauv. (3.90µm). The apertures were more (34) and larger (6.45µm) in I. nil (Linn.) Roth and I. involucrata P. Beauv. While I. cairica (Linn.) Sweet had the smallest apertures (0.94µm). I. pes-capre (Linn.) Sweet had the fewest apertures (16).Data from spine length, spine base, exine thickness, aperture number and aperture diameter helped to delimit I. muricata and I. pes-capre while aperture diameter and number, spine length and exine thickness delimited I. cairica and I. velutipes from the other species of Ipomoea examined in this work.
Palynology can be defined as the branch of science concerned with the study of fossil and living palynomorphs. The term Palynology was coined by Hyde and Williams (1944). Palynomorphs include microscopic plant and animal structures composed of sporopollenin, chitin, or related compounds that are highly resistant to most forms of decay other than oxidation. They are abundant in most sediments and sedimentary rocks, and are resistant to the routine pollen-extraction procedures including strong acids, bases, acetolysis, and density separation. Most palynomorphs are between 5–500 µm in size. Examples of common palynomorphs include: Cryptospores, Embryophyte Spores, Pollen, Dinoflagellates and Megaspores (Evitt, 1963). Earlier pollen researchers were Früh (1885), who enumerated many common tree pollen types, and a considerable number of spores and herb pollen grains. Pollen is produced in the ‘microsporangium’ (contained in the anther of an angiosperm flower, male cone of a coniferous plant, or male cone of other seed plants). Pollen grains come in a wide variety of shapes (most often spherical), sizes, and surface markings characteristic of the species. Pollen grains of pines, firs, and spruces are winged. The smallest pollen grain, that of the forget-me-not (Myosotis spp.), is around 6 µm (0.006 mm) in diameter. Wind-borne pollen grains can be as large as about 90–100 µm (Pleasants, et al., 2001).
One of the first palynological studies on the Convolvulaceae was made by Hallier (1893). He endeavoured to make a natural system of classification on the basis of external morphology and anatomy. However he accorded importance to the gross pollen morphological characters and divided the family into two groups: “Psiloconiae” and “Echinoconiae.” The pollen grains in the “Psiloconiae” are either psilate or with granulated surfaces e.g., Convolvulus, Evolvulus, Jacquemontia, Operculina. The “Echinoconiae” group consists of genera such as Argyreia, Ipomoea, where the pollen grains possessed spines. According to Lawrence and George (1951), Convolvulaceae comprises 50 genera and 1200 species or more. It is represented in Egypt by Nine genera (excluding Cuscuta) with 41 species (Boulos, 2002). The family Convolvulaceae is a eurypalynous family (Erdtman, 1952). Erdtman (1963) regarded that Convolvulaceae is one of many families which need further pollen morphological investigation for taxonomical studies. Large pollen grains of Ipomoea and allied genera would be particularly suitable for studies in morphogenetics, sporoderm stratification and fine structure. The genus Ipomoea comprises the largest number of species within the family Convolvulaceae (Morning glory) which are widely cultivated as ornamentals because of their showy and beautiful flowers. Throughout the world; Ipomoea is usually estimated to contain more than 600 species in which over half of them are concentrated in the Americans and Asian countries (Judd, Campbell, Kellogg, Stevens, Donoghue, 2002). According to Hutchinson and Dalziel (1968), Ipomoea is represented by 37 species in Nigeria. However, a recent study shows that Ipomoea is represented by 34 species which are widely distributed among the savanna-north, forest-south, forest-savanna, forest and the savanna climatic zones of Nigeria (Ogunwenmo, 2003).
1.1 Economic Importance of Ipomoea
Most species have spectacular, colourful flowers and are often grown as ornamentals, and a number of cultivars have been developed. Their deep flowers attract large Lepidoptera such as the pink-spotted hawk moth (Agriuscingulata). Peonidin, an anthocyanidin potentially useful as a food additive, is present in significant quantities in the flowers of the ‘Heavenly Blue’ cultivars. Humans use Ipomoea for their content of medical and psychoactive compounds, mainly alkaloids.
1.2 Uses of Pollen
In forensic biology, pollen can tell a lot about where a person or object has been, because regions of the world, or even more particular locations such as certain sets of bushes, will have a distinctive collection of pollen species (Bryant, 2007). Pollen evidence can also reveal the season in which a particular object picked up the pollen (Stackhouse, 2003). Pollen has been used to trace activity at mass graves in Bosnia (Wood, 2004), catch a burglar who brushed against a Hypericum bush during a crime, (Mildenhall, 2006) and has even been proposed as an additive for bullets to enable tracking them (Wolf, 2008).
1.3 Aims and Objectives
The aim of this work is to study the pollen morphological characters of some common members of the Genus Ipomoea found in Akwa Ibom Statewhich may provide valuable data for the systematic treatment of the genus.
The objectives include;
- To study the pollen shape, size, apertures, exine, sculpture and spine.
- To delimit the taxa using the data obtained.
1.4 Significance of Study
The information obtained will provide taxonomic data for current review of the taxa from Nigeria.