Louis P. Ronse Decraene

THELIGONUM CYNOCRAMBE : DEVELOPMENTAL MORPHOLOGY OF A PECULIAR RUBIACEOUS HERB

The annual Mediterranean herbTheligonum cynocrambe shows a peculiar combination of morphological characters, e.g., switch from decussate to spiral phyllotaxis with 90–100° divergence, combined with a change from interpetiolar to lateral stipules, anemophily, lack of calyx, flowers often dimerous to trimerous, corolla fused in both male and female flowers, male flowers extra-axillary, with 2–19 stamens per flower, female flowers axillary, with inferior uniovulate ovary, basilateral style and perianth, nut-like fruits with elaiosome. In male flowers the androecium emerges as an (uneven) elliptical rim with a central depression. This common girdling primordium is divided up into several stamen primordia. In male flowers with low stamen number the stamen primordia may occupy the corners alternating with the corolla lobes. There are no epipetalous androecial primordia that secondarily divide into stamens. Male flowers occasionally show a hemispherical base that may be interpreted as remnant of the inferior ovary. In female flowers a ring primordium grows into a tube on which the petal lobes arise. The perianth and style become displaced adaxially by uneven growth of the inferior ovary. The ovary is basically bilocular. The lower region of the ovary is provided with a septum that is overtopped and hidden by the single curved ovule.Theligonum is referred to theRubiaceae-Rubioideae, with theAnthospermeae andPaederieae as most closely related tribes.

Pseudodiplostemony, and its implications for the evolution of the androecium in the Caryophyllaceae

The androecium of the Caryophyllaceae is varied, ranging from a two-whorled condition to a single stamen. A number of species belonging to the three subfamilies, Caryophyl-loideae, Alsinoideae and Paronychioideae have been studied ontogenetically with the SEM to understand their peculiar androecial development in the broader context of the Caryophyllales alliance. Although patterns of initiation are highly variable among species, there are three ontogenetic modes of stamen initiation: all stamens simultaneous within a whorl, the antepetalous stamens simultaneous and the antesepalous sequentially with a reversed direction, or both whorls sequentially with or without a reversed direction. The most common floral (ontogenetic) sequence of the Caryophyllaceae runs as follows: five sepals (in a 2/5 sequence), the stamens in front of the three inner sepals successively, stamens opposite the two outermost sepals, five antepetalous stamens (simultaneously or in a reversed spiral superimposed on the spiral of the antesepalous stamens), five outer sterile (petaloid) organs arising before, simultaneously or after the antesepalous stamens, often by the division of common primordia. A comparison with the floral configurations of the Phytolaccaceae and Molluginaceae indicates that the outer petaline whorl of the Caryophyllaceae corresponds positionally to the alternisepalous stamens of somePhytolacca, such asP. dodecandra. The difference withP. dodecandra lies in the fact that an extra inner or outer whorl is formed in the Caryophyl-laceae, in alternation with the sepals. A comparable arrangement exists in the Molluginaceae, though the initiation of stamens is centrifugal. A comparison of floral ontogenies and the presence of reduction series in the Caryophyllaceae support the idea that the pentamerous arrangement is derived from a trimerous prototype. Petals correspond to sterillized stamens and are comparable to two stamen pairs opposite the outer sepals and a single stamen alternating with the third and fifth sepals. Petals are often in a state of reduction; they may be confused with staminodes and they often arise from common stamenpetal primordia. The antesepalous stamen whorl represents an amalgamation of two whorls: initiation is reversed with the stamens opposite the fourth and fifth formed sepals arising before the other, while the stamens opposite the first and second formed sepals are frequently reduced or lost. Reductive trends are correlated with the mode of initiation of the androecium, as well as changes in the number of carpels, and affect the antesepalous and antepetalous whorls in different proportions. It is concluded that the androecium of the Caryophyllaceae is pseudodiplos-temonous and is not comparable to diplostemonous forms in the Dilleniidae and Rosidae. The basic floral formula of Caryophyllaceae is as follows: sepals 5—petals 5 (sterile stamens)—antesepalous stamens 3+2—antepetalous stamens 5 gynoecium 5.

Similarities in Floral Ontogeny and Anatomy between the Genera Francoa (Francoaceae) and Greyia (Greyiaceae)

A comparative study of the floral ontogeny and anatomy of Francoa, with one species, and Greyia, with three species, is made. Flowers arise nearly synchronously on terminal raceme‐like inflorescences with abortive growing tip. In Greyia, development of flowers shows a tendency toward monosymmetry, expressed in the initiation sequence of floral organs. Both genera are weakly obdiplostemonous by a later displacement of antepetalous stamens (“secondary obdiplostemony”), and they develop a comparable semi‐inferior, strongly grooved ovary with axile placentation. The staminodial nature of nectaries is rejected for both genera. The floral ontogenetic, anatomical, and morphological similarities of the two genera are obvious and are consistent with the proposal for a close relationship between Greyia and Francoa supported by molecular data.

The Uncertain Systematic Position of Symplocos (Symplocaceae): Evidence from a Floral Ontogenetic Study

Recent molecular analyses show considerable variation in family interrelationships of Ericales sensu lato. Here, we will review the proposed phylogenetic relationships of the monogeneric Symplocaceae on the basis of floral morphological evidence. Scanning electron microscopy observations of the floral development of Symplocos paniculata Miq. show that some characteristics that were used to determine the position of the family seem to have been misinterpreted by different authors: placentation and number and position of the ovules in the species studied differ from general descriptions of the genus; the reported presence of bracts and bracteoles in all members of the family needs to be confirmed. From a floral ontogenetic point of view, it seems reasonable to consider Symplocaceae to be a member of Ericales sensu lato, where most of the apparently related taxa are classified.

The questionable relationship of Montinia (Montiniaceae): evidence from a floral ontogenetic and anatomical study.

The systematic position of Montiniaceae remains uncertain: a relationship with Cornales has been suggested on phytochemical and embryological evidence, while molecular data point to a relationship with Solanales. We investigated the floral development and anatomy of the South African Montinia caryophyllacea to add a new set of characters for clarifying the systematic position of the family Montiniaceae. Pistillate inflorescences show a higher degree of reduction than staminate, with flowers set terminally on short lateral branches. Flowers have an irregular initiation sequence, with frequent abortions of organs. In Montinia, petals grow rapidly, and no zonal growth takes place. The gynoecium develops as a pit surrounded by a girdle. Placentation is basically parietal and becomes axillary by the postgenital fusion of placental lobes; unitegmic ovules are arranged in two parallel rows with adjacent ovules partly overlapping each other. Unisexuality is respectively attained at the stage of anther development and carpel initiation. The floral anatomy of pistillate and staminate flowers is illustrated and discussed. Observations on Montinia are compared with data of taxa from Saxifragaceae sensu stricto, Cornales, and Solanales. The absence of sympetaly in Montinia is discussed. Morphological and anatomical evidence points to a high similarity with Escalloniaceae. Although a position in the asterids is most probable, there is little support for the relationship with Solanales indicated by molecular data.

Floral Ontogenetic Evidence in Support of the Willdenowia Clade of South African Restionaceae

Willdenowia clade of Restionaceae was studied to understand patterns of reduction of floral elements and sample evidence for discussing the relationships of the group. All species studied are characterized by a concordant reductive trend involving the retardation/reduction of the perianth, the loss of the anterior carpel and the displacement of the remaining carpels, linked with a strongly compressed spikelet. Different modes of carpel reduction, such as a progressive or immediate loss, or fusion of two neighboring carpels, are presented and discussed. The most parsimonious event of gynoecium evolution for the Willdenowia clade is either the sterilization of two carpels in an originally trimerous gynoecium, followed by the loss of the anterior carpel, or the sudden loss of the anterior carpel, preceeding the sterilization of one lateral carpel. The concordant development of the taxa of the Willdenowia clade supports a one-time loss of a carpel and the homogeneity of the clade.

The floral development of Pleuropetalum darwinii, an anomalous member of the Amaranthaceae

Summary The genus Pleuropetalum differs from the Amaranthaceae in its higher stamen and carpel number, coupled with numerous ovules. The floral development of Pleuropetalum darwinii is investigated with the SEM and is compared with the Amaranthaceae and other taxa of the Caryophyllales. Inflorescences are cymose with reduced partial inflorescences. Bracteoles are closely associated with the flower only separated by a short pedicel. Sepal initiation follows a 2/5 sequence but there is an important lag between the first two and the remaining sepals. The androecium arises on a circular primordium; the first four stamens are initiated as pairs opposite the two outer sepals, and are followed by paired or single stamens opposite the inner sepals. However, the number of stamens can fluctuate, or their sequence may be variable. The gynoecium starts its growth as a ring primordium with a number of apices enclosing a flattened apical dome. In early stages septal tissue can sometimes be observed. The central dome becomes completely subdivided in different sectors on which a large number of coiled ovules arise centrifugally. The development of flower and androecium shows similarities with other octandrous Caryophyllales, especially Phytolacca. The shared development is interpreted as a primitive feature. A comparison with other Amaranthaceae on the one hand, and with the Caryophyllales on the other shows evidence that a pluristaminate androecium with outer stamen pairs is plesiomorphic in the Amaranthaceae.

On the wood and stem anatomy of Monococcus echinophorus (Phytolaccaceae s.l.)

Wood of the Australian monotypic genus Monococcus is characterised by short, narrow vessel elements, simple and non-bordered perforation plates, alternate vessel pitting, short fibres with vestigial pit borders, scanty axial parenchyma, and multiseriate rays mainly composed of upright/square ray cells. Styloids are most abundantly present in the secondary phloem. Moreover, secondary growth produced by successive cambia occurs in woody stem parts. These data are compared to other Phytolaccaceae s.l. and a close relationship between Monococcus, Rivina and Petiveria (Rivinoideae or Rivinaceae) is confirmed. However, data on a wider range of taxa are required to support a separation of Rivinaceae from Phytolaccaceae s.s. on the basis of stem anatomy. The presence or absence of successive cambia represents useful taxonomic information for evaluating phylogenetic relationships in Phytolaccaceae s.l. and Caryophyllales.