Anton Igersheim

Gynoecium Structure and Evolution in Basal Angiosperms

A comparative study on gynoecium structure in basal angiosperms revealed new features relevant to systematics. In addition, based on the new phylogenetic framework on basal angiosperms gained by molecular systematics, an evolutionary evaluation of gynoecial character states has become possible. Angiospermy patterns are diverse and are here tentatively grouped into four types according to the mode of carpel closure: (1) by secretion, without postgenital fusion; (2) with a continuous secretory canal but partial postgenital fusion at the periphery; (3) with an incomplete secretory canal and complete postgenital fusion at the periphery; (4) by complete postgenital fusion. In most basal angiosperms the carpels are free, and the inner space of each carpel is occluded from the outside by secretion and not by postgenital fusion (angiospermy type 1). Correlated with this feature is a pronounced ascidiate shape of the carpels. The carpels tend to be shortly stipitate. In relatively many basal clades with pluricarpellate gynoecia an extragynoecial compitum is present. Stigmas are secretory and tend to have pluricellular papillae. Ethereal oil cells at the surface of the carpels (probably intrusive) are present in Illiciales (including Trimeniaceae), Chloranthaceae, Piperales s.l. (including Aristolochiales), and Acoraceae. Ovule structure is diverse. Ovules are predominantly anatropous. Although Amborellaceae, the phylogenetically earliest branching extant angiosperm, has orthotropous ovules, it is argued that the anatropous condition is basal in angiosperms. Crassinucellar ovules are predominant in basal angiosperms. However, there are apomorphic tendencies toward ovule reduction: weakly crassinucellar (Nymphaeales, some Alismatales), pseudocrassinucellar (Acorales, some Alismatales, some Ranunculales), and tenuinucellar (some Piperales s.l., including Aristolochiales, Rafflesiales, some Alismatales). Lobation of the inner integument and semiannular shape of the outer integument are variously present or absent. They appear to be due to architectural constraints in ovule development and not to constitute archaic features. In contrast to anatropous ovules, orthotropous ovules often have an outer integument that is thinner than the inner one. This may be due to a function of the outer integument in ovule curvature as indicated by molecular developmental genetics. On the other hand, the presence of an outer integument that is thinner than the inner one characterizes the majority of the Piperales s.l. (including Aristolochiales), irrespective of presence or absence of ovule curvature.

A simple method for microtome sectioning of prehistoric charcoal specimens, embedded in 2-hydroxyethyl methacrylate (HEMA)

Abstract A simple method for microtome sectioning of prehistoric charcoal, embedded in 2-hydroxyethyl methacrylate, HEMA (= glycol methacrylate, GMA), is described in detail. Procedures for dehydrating, embedding, polymerization and sectioning are, with the exception of some modifications due to the specific texture of charcoal and the relatively large size of the specimens, identical with those used for recent botanical specimens. The sections can be observed directly under the light microscope without further treatment (e.g. staining). Low costs and the rapidity of preparing slides (completion within 24–36 hours), combined with the superior quality of the sections, makes this method best suitable for species analysis of charcoal specimens with problematic anatomy requiring detailed examination of characteristics.

The Reproductive Structures of the Basal Angiosperm Amborella Trichopoda (Amborellaceae)

Amborella, the putatively basalmost extant angiosperm, is poorly known in its reproductive structures. This study offers new results. Inflorescences are botryoids or panicles with accessory flowers in the lower bracts. Flowers are small. Floral phyllotaxis is spiral throughout. The flower base forms a shallow cup that tears into irregular lobes when the flower opens and expands so that the inner floral organs are presented on a flat plate. The flowers are functionally unisexual but they have a bisexual organization, as the female flowers regularly have one or two staminodes outside of the gynoecium. Female flowers have fewer organs than male ones and are slightly smaller. Floral organ number is variable. Male flowers have nine to 11 tepals and 12 to 21 stamens; female flowers have seven to eight tepals, usually one to two staminodes, and usually five carpels. The stamens have a short filament, a triangular introrse anther with two bulging disporangiate thecae that dehisce longitudinally, and a small (secretory?) connective protrusion. The staminodes of the female flowers superficially look like stamens. However, the connective protrusion is more or less lacking; sporogenous tissue is differentiated but meiosis does not take place. The carpels are pronouncedly ascidiate and shortly stipitate and have a wet capitate stigma with multicellular protrusions. The surfaces of the inner canal between the stigma and the ovary are appressed to each other but apparently not postgenitally fused, though they are lined with secretion. The single ventral median ovule is bitegmic, crassinucellar, pendant, and orthotropous. The micropyle is formed by the inner integument. The floral vascular system is simple; each organ has a single strand. The carpels develop into drupelets. The pericarp has a thin fleshy outer layer and a pitted sclerified inner layer. The drupelets are scentless and almost tasteless. A tentative list of plesiomorphic floral features is given.

Floral structure of Takhtajania and its systematic position in Winteraceae.

Floral structure of Takhtajania perrieri, the sole species of Winteraceae in Africa/Madagascar, was studied and compared with that in other Winteraceae. Floral organs are in more or less regular whorls, starting dimerous in the outer perianth region and changing to tetramerous and pentainerous in the inner perianth region and androecium. The innermost androecium whorl is often incomplete. The outer tepal pair is congenitally united, and pairs two and three are postgenitally united in their overlapping area in bud. At the transition from the female to the male phase of anthesis the club-shaped stamen filaments are inflated by cell enlargement, accompanied by starch consumption. The dimerous nature of the unilocular gynoecium is confirmed. The normal linear placentae of the two carpels are oblique to almost horizontal, and therefore the gynoecium does not conform to a usual paracarpous gynoecium with parietal placentation. The ovules are larger than those in other Winteraceae. However, the total evidence of floral features clearly shows the position of Takhtajania in the Winteraceae. Within the family it fits best in the Pseuidowinttera/Zygogynun-clade, which is sister to the Tasmannia/Drimys lade.

Stigma of the African Genera Rutidea and Nichallea (Rubiaceae‐Ixoroideae‐Pavetteae): Highly Modified Receptive Surfaces

The tropical African genera Rutidea and Nichallea possess secondary pollen presentation, as do many other Rubiaceae, but the style‐stigma complex shows some special features. Style and stigma form one slender structure that terminates in a fusiform to clavate or broadly elliptic to globose head. The stigma consists of two permanently fused stigmatic lobes, a common enough situation within the Rubiaceae, but it is further differentiated into three zones: a narrow stigmatic base, a stigmatic head, and the free tips of the stigmatic lobes. The pollen‐receptive surfaces are highly modified. They are restricted to the adaxial sides of the free stigmatic tips and to the lines of fusion between the stigmatic lobes, visible as two longitudinal furrows on the style‐stigma complex. Compared to the structure of the style‐stigma complex in other genera of the Rubiaceae with permanently fused stigmatic lobes, a major morphological trend can be observed in Rutidea and Nichallea, notably the displacement of the pollen‐receptive surfaces to the lower regions of the stigma, resulting in spatial separation of the pollen‐receptive and pollen‐presenting surfaces of the style‐stigma complex.