Annick Le Thomas

Phylogeny, Molecular and Fossil Dating, and Biogeographic History of Annonaceae and Myristicaceae (Magnoliales)

Annonaceae and Myristicaceae, the two largest families of Magnoliales, are pantropical groups of uncertain geographic history. The most recent morphological and molecular phylogenetic analyses identify the Asian‐American genus Anaxagorea as sister to all other Annonaceae and the ambavioids, consisting of small genera endemic to South America, Africa, Madagascar, and Asia, as a second branch. However, most genera form a large clade in which the basal lines are African, and South American and Asian taxa are more deeply nested. Although it has been suggested that Anaxagorea was an ancient Laurasian line, present data indicate that this genus is basically South American. These considerations may mean that the family as a whole began its radiation in Africa and South America in the Late Cretaceous, when the South Atlantic was narrower, and several lines dispersed from Africa‐Madagascar into Laurasia as the Tethys closed in the Tertiary. This scenario is consistent with the occurrence of annonaceous seeds in the latest Cretaceous of Nigeria and the Eocene of England and with molecular dating of the family. Based on distribution of putatively primitive taxa in Madagascar and derived taxa in Asia, it has been suggested that Myristicaceae had a similar history. Phylogenetic analyses of Myristicaceae, using morphology and several plastid regions, confirm that the ancestral area was Africa‐Madagascar and that Asian taxa are derived. However, Myristicaceae as a whole show strikingly lower molecular divergence than Annonaceae, indicating either a much younger age or a marked slowdown in molecular evolution. The fact that the oldest diagnostic fossils of Myristicaceae are Miocene seeds might be taken as evidence that Myristicaceae are much younger than Annonaceae, but this is implausible in requiring transoceanic dispersal of their large, animal‐dispersed seeds.

Cladistic analysis and pollen evolution in Annonaceae

Summary To evaluate hypotheses on pollen evolution in Annonaceae, we present a cladistic analysis, using both palynological and non-palynological characters, and including other Magnoliales as outgroups. As previously proposed, the inferred basic pollen type is single (monads) and monosulcate, with granular infratectal structure (interstitium), but with a few nexinal foliations. Permanent tetrads originated in two major lines: the xylopioids, corresponding to part of Walkers Fusaea subfamily but excluding Fusaea, with granular structure and a nexine of fused granules; and the annonoids, corresponding to Walkers Annona subfamily, with columellar structure and a complexly foliated nexine. The single grains of Isolona are secondarily derived from tetrads. Sulculate pollen arose in both monosulcate and inaperturate lines. The genus Polyalthia, which has unusually diverse pollen, appears to be polyphyletic. Columellar structure originated in smooth monosulcates with granular structure, leading to the malmeoi...

Significance of palynology for phylogeny ofAnnonaceae: Experiments with removal of pollen characters

Phylogenetic analyses based on morphology placeAnaxagorea and other taxa with granular monosulcate pollen, as in otherMagnoliales, at the base ofAnnonaceae. Taxa with columellar tetrads, granular tetrads, and inaperturate monads form a derived clade. To test the systematic importance of palynology, we analyzed the data set with pollen characters removed. The result was lower resolution and a different rooting of the family, betweenUvariopsis and other groups with columellar tetrads.Anaxagorea and other monosulcates are higher in the tree, implying that granular monosulcate pollen, laminar stamens, and irregular endosperm ruminations are reversals. This rooting is highly unparsimonious when pollen characters are included, and only weakly supported over theAnaxagorea rooting when pollen is excluded. Together with preliminary molecular analyses, these experiments confirm the special value of palynology in systematics ofAnnonaceae.

Pectin distribution pattern in the apertural intine of Euphorbia peplus L. (Euphorbiaceae) pollen

Abstract. The apertural inner layer (intine) of Euphorbia L. pollen grains has a characteristic but original structure that has paired thickenings, one on either side of the colpus. To determine the nature and role of this intine layer, pollen grains of Euphorbia peplus L. were germinated in vivo and in vitro. The germination process involves wall changes that facilitate formation of the pollen tube and its subsequent growth. In the thickenings of the intine of E. peplus, the unesterified pectin epitopes are more densely localised in the inner part of the middle intine. No such epitopes are located in the intine portion adjacent to the plasma membrane (cellulosic endintine). Unesterified pectin epitopes are also localised in the outer part of the intine but are restricted to the centre of the aperture, around and in the pore. The de-esterification of pectins is very advanced at the time of dehiscence and pollen germination. The stratification of the aperture intine may take the following pathway at the time of germination: the thin outer zone of the intine in the pore region becomes disorganised and undergoes dissolution with liberation of unesterified and esterified pectins; the middle intine thickenings undergo an important elastic modification, but without liberation of unesterified pectins; the cellulosic inner intine is the progenitor of the pollen tube wall. This special intine of E. peplus is an adaptation to the hydration process preceding germination, increasing intine and pollen grain wall elasticity.

Pollen apertures, exine sculpturing and phylogeny in Iridaceae subfamily Iridoideae

Abstract Specialization from the basic monosulcate and semitectate-reticulate pollen grains of Iridaceae subfamily Iridoideae occurs in all of its four tribes. Disulcate apertures characterize Tigridieae subtribe Tigridiinae (4 genera). Zonasulculate grains occur in two derived species of Cipura (Tigridieae subtribe Cipurinae) and Dietes iridoides (Irideae subtribe Iridinae), all three autogamous. Aperture membranes are typically smooth, but are verrucate in Alophia (Cipurinae), a condition evidently apomorphic for the genus. Operculate apertures occur in Hermodactylis and Iris reticulata (subgenus Hermodactyloides) and there appears to be a gradation in the subgenus to a zonasulculate condition as found in I. danfordiae. While a fairly uniformly reticulate exine predominates in Iridoideae, a trend towards microreticulate or reticulo-rugulate exine is evident. This is accomplished in Gelasine by elongation of the muri and narrowing of the lumina, and by thickening of the muri in Ennealophus and Herbertia. Notable increase in lumina size characterizes some species of Moraea, and the species of Cipura and Dietes in which the grains are zonasulculate. Lumina of sharply different sizes are a notable feature of the exine of Isophysis (Isophysidioideae) and the species of Cypella sometimes segregated as Hesperoxiphium. We conclude that variability in both apertures and exine sculpturing is sufficiently great in the larger genera of Tigridieae and Irideae, and in some smaller ones as well, that palynological data should be sought routinely in systematic and phylogenetic studies in the two tribes. A smaller degree of variation in Mariceae makes it seem less useful to include such studies here. Data from this and other palynological investigations of the Iridoideae indicate that at least at the tribal level for Tigridiinae, and at the generic level for Alophia (and possibly Ennealophus and Gelasine), pollen characters provide valuable synapomorphies for taxon delimitation.

Pollen Diversity and Evolution in Myristicaceae (Magnoliales)

Myristicaceae consist of 21 genera and nearly 500 species of lowland rainforest trees with a pantropical distribution. This article presents new scanning electron microscopy observations on pollen of 13 genera, including all Asian genera, which had previously received very little attention from palynologists. While confirming that all Myristicaceae have monoaperturate pollen shed as monads with a sculptured aperture membrane, this study increases our knowledge of the diversity of pollen shapes, aperture shapes, tectal sculpture and microsculpture, and infratectal structure across the family. It also clarifies a few characters in previously investigated Afro‐Malagasy taxa. These results are discussed in the context of a recent phylogenetic study. While several pollen characters appear to be homoplastic, aperture shape, tectal sculpture, and infratectal structure seem to be of great phylogenetic value in Myristicaceae and clearly distinguish an Afro‐Malagasy clade of five genera (including Mauloutchia) from the rest of the family. Contrary to previous assumptions on character polarity, the ulceroid aperture shape and mixed (to granular) infratectum of most species in this clade both appear to be derived features, whereas the common ancestor of Myristicaceae likely was characterized by sulcate pollen with a columellar infratectum. A continuous tectum also clearly sets apart the members of this Afro‐Malagasy clade from the rest of the family, which has a reticulate to rugulate tectum. However, the status of this character in the ancestor of Myristicaceae remains equivocal.

Taxonomic significance of sporoderm structure in pollen of Euphorbiaceae: Tribes Plukenetieae and Euphorbieae

A pollen sporoderm study of tribe Plukenetieae - subtribe Tragiinae and tribe Euphorbieae was carried out. Most of the species of subtribe Tragiinae examined have a reduced exine, with a perforate tectum, short and irregular columellae, and a thin, undulated or absent foot layer. The endexine is homogeneous, fissured or spongy. The intine is well developed, thicker than the exine, and usually three-layered. In the apertural region both ectexine and endexine are present but are fragmented and disorganised. Only in the clavate-baculate pollen of Tragia volubilis is the exine well-developed and the intine thinner than the exine. The thicker intine is correlated with a thin and weakly developed exine that may provide support, compensating for the severe reduction of the foot layer and the poorly developed, fissured and spongy endexine. The pollen morphology of tribe Euphorbieae is concordant with the common pollen type in the genus Euphorbia . Nevertheless the pollen grains of this tribe have a particular apertural system, that includes modifications to the ectexine, endexine and intine at different aperture levels. The most important observation was the unusual intine with two thickenings that run along each side of the aperture. In general, pollen of the Euphorbiaceae has a thick and well-developed intine. This intine may be uniformly thickened around the grain or may form a lens-shaped structure (oncus) beneath the apertures. Intine thickenings such as those described for tribe Euphorbieae are unknown elsewhere in the family. The more specialised apertural structure, described for tribe Euphorbieae, supports the circumscription of this tribe.

Polygamie chez Atriplex halimus L. (Chenopodiaceae)

Abstract It appears that up to now the inflorescence and flower morphologies of Atriplex halimus have been described incompletly. This species has been classified as monoecious or dioecious. Numerous observations and ontogenic studies have pointed to types of flowers morphologically and functionally hermaphroditic, never described until now. One specimen of this species presents both unisexual, male and female flowers and bisexual flowers, so Atriplex halimus is polygam and more precisely trimonoecious. Observation of inflorescences reveals a structure based on the spike and the dichasium. The sex distribution along the inflorescence axis was studied and the existence of a physiological gradient controlling its expression is discussed.

Pollen ultrastructure and relationships of Fusaea (Baillon) Safford and Duguetia A. Saint-Hilaire (Annonaceae)

Cladistic analyses indicate that the neotropical genus Fusaea, placed by Walker in his Fusaea tribe along with other genera with large, granular tetrad pollen (e.g. Xylopia, Cananga), does not belong with these genera (our xylopioid clade) but rather with several genera with pseudosyncarpous fruits (Letestudoxa, Duguetia, Pachypodanthium), which together with Uvaria and Toussaintia form our uvarioid clade. TEM observations show that despite the convergence of its pollen with the xylopioids at the LM level. Fusaea differs from that group and resembles other uvarioids in having a nexine consisting of multiple foliations rather than fused granules, plus an unusually thick tectum overlying a thin granular layer. TEM observations confirm that two species of Duguetia have a highly reduced exine consisting a probable remnants of the tectum. Cladograms confirm a trend for exine reduction in the uvarioids, with the spines of Pachypodanthium derived from tectal verrucae, as in Letestudoxa and Duguetia. Radiation of the uvarioids was apparently centered in Africa and South America when the South Atlantic was narrower than it is today.

An approach to the knowledge of pollen and allergen diversity through lipid transfer protein localisation in taxonomically distant pollen grains

The aim of the present study is to localise non‐specific lipid transfer proteins (nsLTPs), obtained from Rosaceae (Prunus persica (L.) Batsch) in pollen grains of taxonomically distant plants, such as Iridaceae (Aristea latifolia G.J. Lewis), Platanaceae (Platanus acerifolia (Aiton) Willd.) and Urticaceae (Parietaria judaica L.), in order to compare pollen and nsLTP diversity. A combination of transmission electron microscopy, immunocytochemical techniques, and rabbit specific antiserum against peach nsLTPs (Pru p 3) were used. Abundant labelling to Pru p 3‐like proteins was observed in the cytoplasm, walls and pollenkitt of A. latifolia pollen grains. The presence of nsLTPs associated with the pollenkitt proves that it takes part in the defence mechanism of pollen grains. The labelling was less intense in the cytoplasm and walls of P. acerifolia. Immuno‐stained gold particles were associated with the vacuoles, lipid inclusions, endoplasmic reticulum and Golgi complex. No significant labelling was found in the P. judaica pollen grains incubated with anti‐Pru p 3 polyclonal antibodies. These results indicate important variations in the nsLTPs of different pollen species. Consequently, no taxonomic relationship between pollen grains and nsLTPs could be established.