Pollen morphology of Adenandra (Rutaceae: Diosminae) and its taxonomic implications

The pollen morphology of Adenandra Willd. (Rutaceae: Diosminae) was investigated to determine its taxonomic significance. Pollen of 27 of the 30 infrageneric taxa (representing 16 of the 18 species) was investigated by LM, SEM and TEM. Adenandra differs from all other Diosminae in having 4-colporate rather than 3-colporate pollen grains. This supports the alleged monophyletic status of the genus. Exine morphology and structure, however, is extremely diverse considering the size of the genus, with eight distinct pollen types and four subtypes being discerned. In some members the grains have uniform macroreticulate, striate or striato-reticulate sculpturing, whereas in others the poles have striate, striato-reticulate or reticulate-perforate sculpturing with various types of reticulate or rugulate sculpturing at the mesocolpia. Taxonomic groupings revealed by the pollen characters suggest elationships between taxa that were not previously apparent. It is suggested that evolutionary diversification among species of Adenandra is often more strikingly reflected by pollen morphology than by macromorphology, hence the eurypalynous state of the genus.     

POLLEN MORPHOLOGY AND SYSTEMATICS OF SIPHONOGLOSSA SENSU LATO (ACANTHACEAE)

Pollen morphology of 15 species of Siphonoglossa and of two closely related groups was investigated. Two tribal-specific pollen types are found within Siphonoglossa sensu lato suggesting that the genus is artificial, composed of taxa belonging in several genera among two tribes (subtribes sensu Bremekamp) of Acanthaceae. Five taxa currently included in an informal subgeneric category of Siphonoglossa have tricolporate, prolate pollen (termed Type I) that is characteristic of Odontonemeae (= Odontoneminae, Justicieae). Pollen of the remaining taxa, belonging in two formal sections of the genus, are mostly 2-porate, bilateral (Type II) with a sexine sculpturing characteristic of Justicieae (= Justiciinae). Pollen of section Siphonoglossa is rather uniform, 2-porate, bilateral with lolongate pores, and seem to delimit a natural group. Taxa of section Pentaloba have a more heterogeneous pollen morphology, mostly 2-porate, bilateral with lalongate pores. Controversial aspects of the interpretation of pollen morphology in Justiciinae are presented and their relevance to this study are examined. Hypothetical trends in the evolution of pollen of Justiciinae are discussed and the application of pollen morphology to taxonomy of the genus is presented, including a recommendation for narrowing the generic concept of Siphonoglossa to the taxa of the type section.     

Pollen morphology of Brazilian Fevillea (Cucurbitaceae)

Pollen morphology of the five Brazilian species of the genus Fevillea (F. bahiensis, F. cordifolia, F. passiflora, F. pedatifolia, and F. trilobata) was studied using light and scanning electron microscopy. Pollen in these species is generally stenopalynous, which is in agreement with observations in previous studies of other species. Pollen is shed in monads and characterised by being isopolar, radially symmetric, prolate, and striate. Pollen is of medium size, tricolporate, with long and narrow colpi, a circular endoaperture and a reduced polar area. The exine is up to 2 μm thick.     

Pollen morphology of the Pavetteae (Rubiaceae,Ixoroideae) and its taxonomic significance

Pollen grains of the tribe Pavetteae (Rubiaceae, subfamily Ixoroideae) are examined using LM and SEM. Grains are 3‐ or 4‐colporate and (semi‐) tectate (in one Versteegia species atectate). Sexine patterns vary between perforate, microreticulate, reticulate, rugulate and striato‐reticulate. Supratectal elements are sometimes present. The variation in pollen morphology in the Pavetteae allows to recognize seven pollen types, the distribution of which is useful to evaluate generic delimitations and relationships within the tribe. Pollen characters corroborate the close relationships between the genera Coleactina, Dictyandra and Leptactina and between Homollea, Homolliella and Paracephaelis. All the genera of the tribe proved to be stenopalynous (the species examined possess the same pollen type), except Pavetta, Rutidea, Versteegia and Tarenna which are eurypalynous. In the huge genus Pavetta the existing infrageneric classification is supported pollen morphologically. Pollen morphology further indicates that the genus Tarenna is badly delimited and strongly in need of a revision. The small genus Versteegia is in need of further taxonomic and palynological study to understand the pollen morphological variation encountered here. At a higher rank, pollen morphology also does not contradict the recent division of the Pavetteae in the Ixoreae (a stenopalynous tribe with presumably primitive pollen) and the Pavetteae sensu stricto (eurypalynous).     

Pollen morphology of Diosma and Coleonema (Rutaceae: Diosminae) and its taxonomic implications

The pollen morphology of Diosma and Coleonema of the taxonomically problematic subtribe Diosminae (Rutaceae) was investigated to determine its taxonomic relevance. Pollen of 26 of the 28 species of Diosma and of each of the eight species of Coleonema was investigated by LM, SEM and TEM. In pollen of Diosma the exine sculpturing is uniform, and only one pollen type, reticulate, could be distinguished. In contrast, exine sculpturing shows interspecific variation in Coleonema and three distinct types, striate, reticulate and perforate, could be discerned. Species groupings indicated by the pollen types suggest possible relationships between species within Coleonema and with other genera that were not previously apparent. Pollen data support macromorphological evidence that suggests the generic re-classification of the Diosminae.     

POLLEN MORPHOLOGY IN THE GENUS ERYTHRONIUM (LILIACEAE) AND ITS SYSTEMATIC IMPLICATIONS

Pollen morphology was examined in 40 samples from 19 species in the genus Erythronium (Liliaceae) using scanning (SEM) and transmission electron microscopy (TEM). Pollen grains are monosulcate monads, except for a plant of E. oregonum which has dyad grains. North American and European species are characterized by reticulate exine sculpture composed of various degrees of wavy muri and variably-sized lumina. The most distinctive feature of exine sculpture in the genus is exhibited by the Asian species E. japonicum, which has a unique reticulate pattern composed of striate muri and a distinctive exine structure without columellae. The distinctness of E. japonicum pollen suggests that it has specialized in isolation from species in North America and Europe.     

An Ultrastructural Study of Pollen Wall Ontogeny in Silene Pendula

Pollen of 41 species representing all seven genera of the Neottieae were examined by scanning electron microscopy. Except for Lecanorchis, the genera of the Neottieae constitute a natural group based on pollen morphology. Pollen occurs as single grains in the primitive species and in tetrads in the other species. Most grains are monoaperturate, porate or tenuate, and the tetrads often have irregularly shaped grains. Exine structure varies from tectate-perforate to semitectate. Lecanorchis is anomalous among the Neottieae in that it has 0–5, sunken, relatively small pores. Pollen morphology of this genus indicates that it is probably more closely related to the Gastrodieae than the Neottieae. There are at least four basic phyletic units in the Orchidaceae: the Neottioideae, Apostasioideae, Cypripedioideae, and Epidendroideae. These groups are distinguished by the presence of monads in at least their more primitive members and by their unique pollen types.     

Die pollenmorphologie der afrikanischen buxus- und notobuxus-arten (buxaceae) und ihre systematische bedeutung

Pollen grains of 8 African species of Buxus and Notobuxus were examined by light and scanning electron microscopy. Three pollen types are recognized based on the exine sculpture and the evolutionary trends of the pollen characters are discussed. Pollen morphology shows the existence of three major systematic groups. These results support the previous classification of an African section Probuxus with two subsections and speak in favor of the generic rank of the Notobuxus species. Together with anatomical and taxonomical data pollen morphology and its evolutionary trends lend support to the suggestions that the centre of origin of the genus Buxus might have been in Africa, while secondary centres of evolution have developed in the neotropical and Eastasian region.     

Pollen morphology inLinum sect.Macrantholinum

Pollen of the two distylous species which make upLinum sect.Macrantholinum differs from that of other distylous species in the genus in being multiporate and in having much more modest differences in exine sculpturing between grains from long- and short-styled plants. Pollen morphology does not help in relating the two species to others in the genus but does support their retention in a separate section.     

Pollen morphology and taxonomic implications of Muscari Miller (Hyacinthaceae) species from Sicily

Pollen morphology of the native Sicilian species of the genus Muscari, one of which is endemic to Sicily, belonging to the subgenera Muscari, Leopoldia and Pseudomuscari, was studied using a light microscope and a scanning electron microscope. Pollen grains are monads, heteropolar and monosulcate; the exine is semitectate reticulate and perforate. The sulcus extends from distal to proximal face and its length is not directly proportional to the size of the granules and varies from one species to another.     

Systematic implications of pollen morphology in Elsholtzia (Elsholtzieae–Lamiaceae)

Pollen morphology of 18 species (32 specimens) representing all three currently recognized sections of the genus Elsholtzia (Elsholtzieae–Lamiaceae) was investigated in detail using light, scanning electron and transmission electron microscopy. Elsholtzia pollen grains are small to medium in size (P=20–50 μm, E=16–45 μm), mostly prolate‐spheroidal to prolate, and rarely oblate‐spheroidal to subprolate in shape (P/E=0.95–1.46), hexacolpate (the amb more or less circular or ellipsoid) with granular aperture membranes. Three distinct types of sexine ornamentation are observed in Elsholtzia: perforate, rugulose‐bireticulate, and bireticulate. The bireticulate pattern is the most common, showing a wide range of morphological variation among species. The exine thickness varies from 1.2 to 2.5 μm. Among the present palynological data, the variability observed in sexine ornamentation of Elsholtzia could be of systematic significance. Current infrageneric classification of the genus Elsholtzia is partially congruent with pollen morphological data.     

Pollen size in Carex: The effect of different chemical treatments and mounting media

Pollen size and pollen aperture size for ten species of the genus Carex L., native to Estonia, have been measured using light microscopy. The species selected represent different sections of the genus, a range of habitats and different chromosome numbers. The effects of two basic chemical treatments, two mounting media and the effect of chemically induced dehydration with tertiary butyl alcohol (TBA) on the size of pollen grains were then recorded.

In general pollen size and pollen aperture size of the species examined is highly variable at both intraspecific and interspecific levels. Carex hirta has notably larger pollen grains than any of the other species investigated and, although correlations between size and chromosome number in the species examined are limited, it also has the highest chromosome number. Statistically significant size differences resulted from variations in chemical treatment, mounting media and tertiary butyl alcohol (TBA) induced dehydration. Acetolysed pollen grains are larger than potassium hydroxide (KOH) treated pollen grains. Pollen grains dehydrated after chemical treatment with TBA are larger than pollen grains not dehydrated. Pollen grains mounted in silicon oil are smaller than grains mounted in glycerine. But considering the great size variation of Carex pollen grains, the size changes caused by preparation procedures fall within the size variation range of the species examined.

All the samples contained a high number of deformed pollen grains and pollen grains with hardly distinguishable or no lateral apertures.     

Pollen morphology of the genus Euphrasia L. (Orobanchaceae) from Pakistan and Kashmir and its taxonomic significance

Pollen morphology of 25 species of the genus Euphrasia L., belonging to the family Orobanchaceae from Pakistan has been examined by light and scanning electron microscope. It is a stenopalynous genus. Pollen grains are usually radially symmetrical, isopolar, tricolpate, sub-prolate to prolate-spheroidal rarely oblate-spheroidal. Sexine slightly thinner than nexine or as thick as nexine. Tectum coarse to fine retipilate or rugulate–retipilate. On the basis of exine ornamentation three distinct pollen types viz., Euphrasia foliosa, Euphrasia multiflora, and Euphrasia incisa are recognized. Pollen morphology is significantly helpful at specific level within the pollen type.     

Pollen morphology in <Emphasis Type="Italic">Lysipomia</Emphasis> (Campanulaceae: Lobelioideae) and interpretation of shape artifacts

The pollen of 32 species of Lysipomia was examined by light, scanning, and transmission electron microscopy. Two pollen types occur in the genus: 3-colporate and 6-colporate. The 3-colporate condition occurs in only two species, L. laciniata and L. pumila. The remaining 30 species are 6-colporate, a condition known from only one other genus in the Campanulaceae. Surface sculpturing among the species is uniformly striate. Pollen shape was highly variable within a single individual in comparisons of pollen gathered from herbarium specimens, FAA preserved material collected in the field, and fresh pollen from cultivated individuals grown from seed. Shape may change from oblate spheroidal to subprolate as a result of drying time and temperature, and should not be used as a morphological character in systematic studies if infraspecific variation is seen. When fresh or preserved pollen is not available, rehydrated pollen should be compared to reduce the possibility of inadvertent artifact production confounding the analysis of morphological data.     

Pollen morphology in the genus Veronica L. (Plantaginaceae) and its systematic significance

Pollen grains of 30, mainly annual, species from 134 populations of the genus Veronica (Plantaginaceae, formerly Scrophulariaceae) from the Mediterranean Region, have been studied with light and scanning electron microscopy. Three pollen types are defined based on pollen size and exine surface sculpture. In some cases within the study group pollen size can be useful in species determination. Hypothetical relationships of pollen grain size and aperture number with ploidy level, style length and corolla diameter are discussed. The ornamentation of the exine in Veronica, although generally a conservative character within the genus, gives some additional support to the most recent infrageneric classification of Veronica.     

Pollen morphology of Astragalus section Hymenostegis (Fabaceae) and evaluation of its systematic implications

Astragalus is with nearly 3000 described species the largest genus of flowering plants. So far analyses of pollen characters have only been conducted for a few species of the groups within the genus. Here we analyse pollen grains of 22 species representative for Astragalus section Hymenostegis using scanning electron microscopy. We found the basic shape of the pollen grains to be oblate-spheroidal and apertures to be tricolpate as for other eudicots. The sculpturing pattern of the exine is micro-reticulate. Pollen grains show low morphological variation among different species of this section, but differences occur between sections of the genus. We conclude that the vast morphological differentiation that occurred during the rapid radiation of section Hymenostegis was not accompanied by comparable differentiation in pollen morphology.     

The palynology of the genus Rondeletia L. (Rubiaceae-Cinchonoideae-Rondeletieae)

Pollen of 20 species of Rondeletia, covering three subgenera and seven sections or “species groups” of the genus, was studied using light and scanning microscopy. Rondeletia, characterized by binucleate mature pollen grains like numerous other Rubiaceae, was found to be eurypalynous. The pollen is isopolar and small-sized (average equatorial diameters 11.4–22.8 μm) and 3-colporate (rarely 4-colporate). In equatorial view, the pollen grains are mostly ± spheroidal (rarely suboblate); in polar view (ambitus), they are mainly circular or semiangular (intersemiangular in one species only). Three different exine types are distinguishable: exine with 1) tectum minutely perforate, perforations usually isodiametric, 2) tectum with comparatively large, not isodiametric perforations or 3) coarsely reticulate; supratectal sculpturing elements are lacking; the width of the perforations and lumina is either equal or different at the apo- and mesocolpia; in a few species rod-like luminal processes are present. Palynological features of most of the investigated taxa tend to overlap so that palynology is not very helpful in supporting the subgeneric division of Rondeletia. It was, however, noted that pollen morphology, to some extent, supports the sections of subgen. Arachnothrix. Palynologically, the subgen. Rogiera was found to be heterogeneous in that each of the three investigated species is characterized by a different exine type; one of these, R. strigosa, differs from all other Rondeletia species investigated in having a coarsely reticulate exine. R. odorata (subgen. Rondeletia) differs from all other investigated species in its intersemiangular pollen shape.     

LIGHT AND SCANNING ELECTRON MICROSCOPIC STUDIES ON POLLEN OF TETRAPLASANDRA (ARALIACEAE) AND RELATIVES

Pollen of seven species in Tetraplasandra and three species in related genera were studied with light and scanning electron microscopes. A new thin-section technique was employed for the study of exine stratification and apertural structure. This study reveals several previously undescribed pollen structures for the group. Trends toward increase in pollen size and in specialization of other pollen characters are evident in Tetraplasandra. Pollen of Reynoldsia and Peekeliopanax differs from Tetraplasandra in the pertectate sexine and the absence of inner nexinous breaks, respectively. A pollen correlation study shows that Munroidendron falls readily within the genus Tetraplasandra but is distinguishable from the latter by its bifurcate colpi.     

Pollen morphology in Asiatic species ofTrillium

Pollen grains of five species and two interspecific hybrids ofTrillium from eastern Asia have been examined with scanning electron and transmission electron microscopy. All species from eastern Asia, excludingT. govanianum, are characterized by inaperturate pollen and an unstratified and granulated exine structure. Pollen of the Himalayan species,T. govanianum, is, however, monocolpate and intectate. The palynological evidence suggests that the Asiatic species, excludingT. govanianum, are closely related to each other and toT. erectum in North America, andT. govanianum is independent of the other species in the genus.     

Pollen morphology and infra-generic evolutionary relationships in some Chinese species of Pedicularis (Scrophulariaceae)

 The pollen grains of 32 Chinese species of Pedicularis representing 13 groups within the genus were investigated using light microscopy and scanning electron microscopy. The genus is eurypalynous, the apertures may be tricolpate, trisyncolpate, or bisyncolpate and five types of surface ornamentation (microscabrate, microrugulate, retipilate, microreticulate and microfoveolate) were observed. Comparison of the different aperture types using light microscopy allows three pollen types to be distinguished. Examination of exine ornamentation with scanning electron microscopy enabled each pollen type to be divided into two or three sub-types (giving a total of seven sub-types). Pollen morphology within the genus is discussed in relation to infrageneric relationships, evolutionary and pollination biology. There is little correlation with the existing infrageneric taxonomy (some taxonomic groups have more than one pollen type, while the same pollen type may be found in several different species-groups), but greater correlation with the corolla morphology. Received January 10, 2002; accepted March 5, 2002 Published online: March 10, 2003