Pollen Morphology of Tribes Gnaphalieae , Helenieae , Plucheeae and Senecioneae ( Subfamily Asteroideae ) of Compositae from Egypt

POLLEN morphology of twenty five species representing 12 genera of tribes Gnaphalieae, Helenieae, Plucheeae and Senecioneae (Asteroideae: Asteraceae) was investigated using light and scanning electron microscopy. The genera are Phagnalon, Filago, Gnaphalium, Helichrysum, Homognaphalium, Ifloga, Lasiopogon, Pseudognaphalium, Flaveria, Tagetes, Sphaeranthus and Senecio. Two pollen types were recognized viz. Senecio pollen type and Filago pollen type. Description of each type, a key to the investigated taxa as well as LM and SEM micrographs of pollen grains are provided.


Introduction
Gnaphalieae, Helenieae, Plucheeae and Senecioneae (Asteroideae: Asteraceae) are of the well represented tribes in Egypt, where 12 genera with about thirty five species are native in the country [1].Reference [2] separated the Compositae pollen into two groups based on the gross morphology of the pollen grain: the liguliflorae-type characterized by echinolophate pollen, which is generally found in the Cichorieae; and the tubuliflorae-type, which is found in many other tribes.Reference [3] recognized three pollen types, i.e., psilate (this type can not be easily recognized), echinate, and lophate pollen.Based on pollen wall ultrastructure, [4] and [5] reconsidered these pollen types and recognized five major pollen wall types, the Helianthoid, the Senecioid, the Arctotoid, the Anthemoid and pollen types without designated patterns.These pollen types are variously distributed among the Cichorioideae and the Asteroideae.Pollen of the Barnasioideae is similar to the echinolophate pollen of the liguliflorae-type, but lacks the spines [6].Reference [7] observed that the pollen grains of some Compositae tribes consist of three compound apertures, each one of them is made up of ecto-, meso-and endo-aperture, the apertural membrane is formed by a foot layer and endexine with complete ectexine granules, the ectoaperture involves the tectum and infratectum, the mesoaper-ture involves the foot layer and the outer layer of the endexine and the endoaperture involves the inner layer of the endoxine.The intine is thickened considerably in Anthemideae near the aperture.Reference [8] described Gnaphalieae pollen as a two-layered pollen sexine with an outer baculae and an inner perforated layer.Reference [9,10] observed that the pollen morphology and anatomy of the Plucheeae correspond to that of the Inuleae; thus, the pollen is echinate and caveate with one layer of baculae between the spines and two baculate layer in the spines bases.This paper considers pollen grains of the tribes Gnaphalieae, Helenieae, Plucheeae and Senecioneae in the flora of Egypt, which may prove of value in systematic treatments.Pollen types that show all the possible characteristic features (shape, size, apertures, wall stratification) are considered, with special reference to the specific characters of each pollen type.The available palynological data will be discussed.

Materials and Methods
Pollen materials were removed from herbarium specimens identified according to [1,11,12] and [13].The specimens were kept in Cairo University Herbarium (CAI) and Herbarium of South Valley University (QNA, proposed abbreviation) (   prepared according to the method of [15] and SEM observations were made on acetolyzed grains coated with a thin layer of gold/palladium for 3 minutes using a EMITECH K550 sputter according to the Erdtman method [16].SEM examined with a JEOL-6300 SEM of Central Lab., Faculty of Science, South Valley University, Qena, Egypt.The terminology used is that of [17,18] and [19].

Results
The subtribes, genera and species of tribes Gnaphalieae, Helenieae, Plucheeae and Senecioneae (according to [14]) that are represented in the flora of Egypt are arranged alphabetically to facilitate consultation.For each species, the valid scientific name is given followed by the citation of the authority and the date of publication.Synonymy is at a minimum to avoid complications.For full synonymy of the species see [1,12] and [13].

Discussion
Palynological characters applied to the species of Gnaphalieae, Helenieae, Plucheeae and Senecioneae in Egypt proved to be useful in the distinction between two groups.The pollen grains are usually 3-zonocolporate or 3-zonocolpororate with lolongate or lalongate (rarely circular) ora.
There is semi-similarity between the pollen grains of the investigated taxa, as a result it will be difficult to make accurate distinguishing and to construct true key between the studied species.Two pollen types are distinguished according to the pollen class.The Senecio pollen type, in which the pollen are 3-colpororate, is characteristic of the species of genera Phagnalon, Helichrysum, Ifloga, Flaveria, Tagetes, Sphaeranthus and senecio.The Filago pollen type, in which the pollen are 3-colporate, is characteristic of the species of genera Filago, Gnaphalium, Homognaphalium, Lasiopogon and Pseudognaphalium.
Ora shape contributes to differentiate between the related species of Helichrysum glumaceum, Ifloga spicata, Flaveria bidentis, Tagetes minuta, Senecio flavus and Senecio vulgaris are characterized by lalongate ora shape, Helichrysum orientale, Homognaphalium pulvinatum and Sphaeranthus suaveolens exhibit circular ora shape, while lolongate ora shape is observed in the remaining studied species.The aperture width also contributes to differentiate all studied species of genus Filago, Ifloga spicata, Senecio glaucus subsp.coronopifolius, S. glaucus subsp.Glaucus and S. vulgaris which exhibit colpi are slightly width at equator, Lasiopogon muscoides and S. hoggariensis which have slender colpi at equator, Senecio aegyptius has narrow colpi at equator from the other investigated taxa which are characterized by wide colpi at equator.It also points to the close relationship between the four Filago species which exhibit very close pollen grains being similar in pollen shape, colpi characters, sculpture and dimensions.
The pollen sculpture is more uniform in most investigated species with perforate texture.The pollen grains are spiny to spinulate with perforate echinae bases.In Gnaphalium uliginosum aperture margins are perforate while in Sphaeranthus suaveolens species they are microreticulate, also in both Filago contracta and Senecio vulgaris perforation restrict to the echinae bases.