Seed morphology and anatomy in someAnnonaceae

Twelve species ofAnnonaceae, namelyAncana sp.,A. stenopetala, Annona cherimola, A. montana, A. muricata, A. squamosa, Bocagea sp.,Bocageopsis canescens, two species ofUnonopsis, Xylopia aromatica, andX. emarginata, were investigated with respect to the morphology and anatomy of the seed. They show the basic structural pattern characteristic of annonaceous seeds: perichalaza, fibrous mesotesta, and rumination developed by both integuments. However, several differential characters, some of them never previously described, were found: All taxa exhibit an additional endotestal mechanical layer which forms the micropylar plug except inAncana. InAncana the plug is built by the inner integument. Aril, sarcotesta and pits on the seed surface are present in some taxa and show different origin and structure. Special anatomical adaptations possibly functioning during germination are described. The results obtained from the investigated taxa are discussed and compared with published data on seed structure inAnnonaceae.     

Seed development and function inArtabotrys hexapetalus (Annonaceae)

Until now seeds ofAnnonaceae were characterized as mesotestal only. The seed ofArtabotrys hexapetalus, however, is meso- and endotestal. An outer mechanical layer which surrounds the seed as a lignified fibrous tissue is derived from the mesotesta. A complex inner mechanical layer develops from a partially multi-layered endotesta built up by crystal-containing stone cells. The multi-layered endotesta forms a prominent seed plug in the micropylar region which is prolonged along both sides of the perichalaza as inner walls. The endotesta is one-layered on the sides of the seed and participates in rumination. In addition the endotesta may serve for deposition of end-products of metabolism. The complex growing process of the perichalaza and its surrounding tissues is described in detail. The perichalazal pad of tanniferous cells forms an U-shaped septum, in conjunction with the endotesta, dividing the seed into two chambers. During seed development it functions as transmitter of nutrients from the outer chamber filled with starch grains to the nucellus, endosperm and embryo contained in the inner one. During germination this pad probably serves for the uptake of water. — At the initial phases of germination the seed dehisces into two valves along the raphal and antiraphal side. Later on an additional parenchymatous operculum covering the seed apex disintegrates and the endotestal plug fixed by its two prolongations splits along a preformed fracture line into two parts to release the seedling. Rudiments of an aril are recognizable in young seeds only. — The data obtained fromArtabotrys hexapetalus are discussed and compared with published information on seeds in other annonaceous taxa. For systematic considerations the necessity to define the origin of the annonaceous seed plug from one or the other integument is emphasized as it may prove to be an important differential character withinAnnonaceae.     

Karyosystematics and evolution of AustralianAnnonaceae as compared withEupomatiaceae,Himantandraceae, andAustrobaileyaceae

Chromosome counts are presented for 12 genera and 20 species of AustralianAnnonaceae (all diploid with 2n = 16 or 18; Table 1) and two species ofEupomatiaceae (2n = 20, partly from Papua New Guinea). Detailed studies on interphase nuclear structure, condensing behaviour of chromosomes, and fluorochrome and Giemsa C-banding patterns also includeHimantandraceae (Galbulimima) andAustrobaileyaceae. — Eupomatiaceae completely correspond withAnnonaceae karyologically, their base number 2n = 20 is interpreted to have evolved from 2n = 18 by ascending dysploidy from common ancestors.Eupomatia laurina andE. benettii differ in DNA and constitutive heterochromatin (hc) quantity; their evolution from high to low DNA content probably corresponds to general progressions inMagnoliidae. Austrobaileya has nuclei of the presumably primitive Tetrameranthus type which is closely related to that ofGalbulimima and several other primitive taxa inMagnoliidae. Karyomorphology and other characters support the maintainance of two main branches within theMagnoliidae, Laurales andMagnoliales, withAustrobaileya probably intermediate; theWinteraceae appear more remote.—InAnnonaceae the reestablishment ofAncana is underlined by its chromosome number (2n = 18) the unexpected and specialized disulcate pollen, and various morphological characters which point to a close alliance with the Australian endemic generaFitzalania andHaplostichanthus (also disulcate) and the American genus pairSapranthus/Desmopsis; they are united in the provisionalSapranthus tribe, with a more distant position toFissistigma s. str. (2n = 16). AustralianAnnonaceae exhibit a high generic and a low species diversity; they can be considered as an ± old and partly impoverished outpost of the family with phytogeographical relationships to Asia, Africa and America.—On the base of field observations three main types of floral development inAnnonaceae are proposed, the most elaborated one found in the fly pollinated genusPseuduvaria. The growth form change from shrubs to lianas during the ontogeny ofDesmos andMelodorum, the vegetative propagation of anAncana species and the ecological and evolutionary patterns of the taxa investigated are discussed.     

Ovular development and morphology in some magnoliaceae species

Floral phenology and ovular development ofLiriodendron tulipifera are described. The ovule primordia are initiated in December, followed by prominent development in March, and the ovules are mature in May. The inner integument is formed as an annular rim on the incurving ovule primordia, but the outer integument develops as a semi-annular rim interrupted on the concave side of the funicle. Later, an outgrowth, which is interpreted here as an obturator, arises on the concave side of the funicle. The funicular outgrowth arises far from the inner integument, while the outer integument is close to the inner. The outer integument and the funicular outgrowth together form an envelope complex. Later the outer integument produces two distal lobes, which disappear at maturity. Mature ovules of the threeMagnolia species examined have similar lobes. It is suggested that the hood-shaped outer integument is primitive in angiosperms.     

Embryology of Siparunaceae (Laurales): characteristics and character evolution

Embryological characters of Siparunaceae, which are poorly understood, were studied on the basis of two constituent genera, an African Glossocalyx and a South American Siparuna, to better understand their evolution within Laurales. These two genera have many embryological characteristics in common with the other lauralean families. Noticeably, they share the multi-celled ovule archesporium (uncertain in Glossocalyx) as a synapomorphy with all the other lauralean families except Lauraceae, the anthers dehisced by valves as a synspomorphy with all the other lauralean families except Calycanthaceae and Monimiaceae, and the bisporangiate anther as a synapomorphy with Gomortegaceae and Atherospermataceae. Siparunaceae are, however, distinct from all other laularean families in having unitegmic ovules that were derived from bitegmic ovules, probably due to an elimination of the outer integument. Likewise, the lack of the testa (i.e., developed outer integument), the "endotegmic" seed coat, and the perichalazal seed at maturity are also characteristics of Siparunaceae. Within the family, Siparuna differs from Glossocalyx in having plural tetrads of megaspores and plural, starchy-rich, one-nucleate, tubular embryo sacs (autapomorphies). On the other hand, Glossocalyx is characterized by having bilaterally flattened seeds (autapomorphy). Although functional aspects of those autapomorphies are uncertain, both Glossocalyx and Siparuna show evolution in different embryological characters.     

How stable are genomes of tropical woody plants? Heterozygosity in C-banded karyotypes ofPorcelia as compared withAnnona (Annonaceae) andDrimys (Winteraceae)

InPorcelia goyazensis (2n = 18) Giemsa C-banding patterns differ from those ofAnnona reticulata (2n = 14) and reveal structural heterozygosity. The amplitude of karyological variation in theAnnonaceae is greater than expected for a primitive woody family. In a comparison with other tropical angiosperm groups, the highly differentiated karyotype ofDrimys brasiliensis (2n = 86) is interpreted as being the end-point of numerous karyological changes.     

Embryogenesis and seed development in Sinomanglietia glauca (Magnoliaceae)

The development of the floral bud, especially the ovule and seed coat, of Sinomanglietia glauca was observed. Floral buds were covered by eight to nine hypsophyll pieces. The hypsophyll nearest the tepal was closed completely and characterized by two arrays of densely stained cells with dense cytoplasm, which split longitudinally at flowering. The perianth consisted of 16 tepals arranged in three whorls. The gynoecium was composed of numerous apocarpous carpels; the ovule was anatropous with two integuments. Embryogenesis was of the Polygonum type, and the endosperm was nuclear. The inner integument degenerated during seed development. The seed of S. glauca had an endotestal seed coat comprised of a sclerotic layer derived from the inner adaxial epidermis of the outer integument and a sarcotesta derived mainly from the middle cells between the inner and outer epidermis of the outer integument. The embryo developed normally, so embryogenesis is not the cause of difficult regeneration.     

Studies in the embryology of the diandrous orchidCypripedium cordigerum (Cypripedieae,Orchidaceae)

The anther wall layers ofCypripedium cordigerum are six to eight. The glandular tapetum is 2- or 3-layered and its cells are uninucleate. Simultaneous cytokinesis results in decussate, isobilateral and tetrahedral pollen tetrads. Ripe pollen grains are 2-celled. The mature ovules are anatropous, bitegmic and tenuinucellate. Both the integuments are dermal in origin and 2-layered. The inner integument alone forms the micropyle. The female gametophyte is 6-nucleate and bisporic. The reduction of nuclei is due to the strike phenomenon. Double fertilization occurs. The primary endosperm nucleus divides to form two free endosperm nuclei. The mature embryo is undifferentiated. The cells ca, m and n contribute to the embryo. The suspensor is single-celled. The seed coat is formed entirely by the outer layer of the outer integument. There are three sterile and three fertile valves in the ovary. In the prefertilization stages these valves consist of parenchymatous cells with starch and raphides. After fertilization, the sterile valves develop sclerotic cells whereas the fertile valves remain parenchymatous. The pericarp structure and embryological features support the retention of tribeCypripedieae within theOrchidaceae.     

Embryology of tribeDrypeteae, an enigmatic taxon ofEuphorbiaceae

The tribeDrypeteae, whose traditional assignment inPhyllanthoideae ofEuphorbiaceae is now doubtful, is studied embryologically on the basis of a literature survey and examination of six additional species in two of the four constituent genera.Drypeteae are characterized by having several embryological features that are unknown in otherPhyllanthoideae, such as a two- or three-celled ovule archesporium; a thin, two cell-layered parietal layer in the nucellus; no nucellar beak or cap; an early disintegrating nucellar tissue; thick, multiplicative, inner and outer integuments; an endothelium; a few discrete vascular bundles in the outer integument; and a fibrous exotegmen (or its derived state). EmbryologicallyDrypeteae do not fit within thePhyllanthoideae and, as available nucleotide sequence data from therbcL gene suggest, are rather placed nearErythroxylaceae, Rhizophoraceae, Chrysobalanaceae, andLinaceae. Drypeteae share with those families a combination of the fibrous exotegmen, the endothelium, and the thick, multiplicative inner integument.     

The embryology ofStegnospermataceae,with a discussion on its status,affinities and systematic position

The embryology ofStegnosperma halimifolium andS. watsonii has been studied in detail. The tapetum is of the secretory type and its cells become multinucleate. Simultaneous cytokinesis in the pollen mother cells follows meiosis. The ripe pollen grains are 3-celled. The ovule is crassinucellate, bitegmic and amphitropous, with the micropyle formed by the inner integument alone. The female archesporium is one celled, and the parietal tissue 3–5 layered. The embryo sac development conforms to thePolygonum type. A central strand, 6 or 7 cells thick, differentiates inside the nucellus and extends from the base of the embryo sac to the chalazal region. The endosperm is nuclear. The embryogeny conforms to the Caryophyllad type. The seed coat is formed by the outer epidermis of the outer integument and the inner epidermis of the inner integument. Based on this evidence and other data, the status of the genus as an independent family,Stegnospermataceae (Stegnospermaceae) is confirmed. Apparently, it forms a connecting link betweenPhytolaccaceae andCaryophyllaceae.     

Comparative structure of ovules and seeds inRafflesiaceae

The genera of theRafflesiaceae show a marked diversity in the structure of their ovules and seeds. Evolutionary trends are recognizable in ovule orientation and number of integuments. A change from anatropous ovules inApodantheae andMitrastemoideae towards incomplete anatropy inRafflesieae and orthotropy inCytineae occurs, next to a change from bitegmic ovules inApodantheae towards unitegmy with rudimentary outer integuments inRafflesieae andCytineae and full unitegmy inMitrastemoideae.—The differences in ovule structure are clearly reflected in the seeds. The seeds are essentially exotegmic, have very small embryos and an oily endosperm.—Seed structure strongly confirms the existing subfamilial classification and supports additional arguments for the generic status ofApodanthes. It does not support a separate status of the genusBerlinianche. InRafflesiaceae, seed micromorphology is only of limited use at the species level. As far as known seed dispersal is endo- or exozoochorous in all genera.     

Structure and development of the ovule and seed in Aristolochiaceae, with particular reference to Saruma

All members of Aristolochiaceae have anatropous, bitegmic, crassinucellate ovules, which are endostomic except in Saruma and Asarum arifolium where ovules are amphistomic. The outer integument is two cell-layered and the inner integument is three cell-layered. The chalazal megaspore is the functional one. All these conditions appear to be plesiomorphic for the order Piperales, which consists of five families, Aristolochiaceae, Hydnoraceae, Lactoridaceae, Piperaceae and Saururaceae. The embryo sac in Aristolochiaceae is eight-nucleate and corresponds to the Polygonum type; a hypostase is frequently present in this family. The seed coat of Aristolochia s.l., Asarum, Saruma and some Thottea species consists primarily of a two cell-layered testa, and a three cell-layered tegmen. In some species the cells of the outer epidermis become radially elongated, forming reticulate wall thickenings. Cells of the inner layer of the testa have crystals and thickened inner walls. The three layers of the tegmen are tangentially elongated, and become cross fibres at maturity, as fibres of the outer and inner layers are parallel to the seed axis, whereas those of the middle layer are perpendicular to it. This type of seed coat anatomy is synapomorphic for Aristolochiaceae. In addition, the gross morphology of the seed and elaiosome histology are remarkably similar in Asarum and Saruma, thus supporting a sister-group relationship between them. Embryological and seed characters do not supply any synapomorphy that support a close relationship between Aristolochiaceae, Hydnoraceae and Lactoridaceae. Instead, some seed features such as the absence of seed appendages and the collapsed cells of endotesta may indicate a close relationship of Lactoris with Piperaceae plus Saururaceae, although this is the subject of further analysis.     

The embryology and relationships ofOliniaceae

Two of the five species ofOliniaceae (Olinia emarginata andO. ventosa), a monotypic and problematic family of theMyrtales, were investigated embryologically.Oliniaceae clearly agree with otherMyrtales in their basic embryological characteristics, and are characterized further by having an ephemeral endothecium, a campylotropous ovule, and a thick, three-five-layered, outer integument. A combination of these three characteristic features is unknown elsewhere inMyrtales, so that embryological features do not support a close relationship with any other member of the order. Shared distinctive anther characteristics (i.e. ephemeral endothecium) suggest thatOliniaceae are derived from the common ancestor ofCrypteroniaceae s. str.,Rhynchocalycaceae, Alzateaceae, andPenaeaceae.     

Biodegradation of Chilean native wood species,Drimys winteri and Nothofagus dombeyi,by Ganoderma australe

Drimys winteri and Nothofagus dombeyi, two native Chilean wood species with high potential for pulp production, were biodegraded by Ganoderma australe. This fungus is known to provoke extensive and selective biodelignification of these wood species in the field. Under laboratory conditions, N. dombeyi underwent higher weight and component losses than D. winteri. In neither case was the lignin removal selective, because glucan loss was almost simultaneous with lignin degradation. The decayed wood chips became progressively discoloured throughout the biodegradation time. The brightness increase was only partly reversed in thermal reversion assays. Nothofagus dombey solubility in 1% NaOH increased by 13.7% after 9 weeks of biodegradation, while D. winteri solubility increased by 14.2% in a shorter period (6 weeks). In both cases, the solubility increase was proportional to the liquor absorbance increase at 272 nm, which indicates that the wood solubility in 1% NaOH was dependent of lignin solubilization.     

Gynoecium and perianth inZanthoxylum s.l. (Rutaceae)

The question whether the uniseriate perianth ofZanthoxylum L. s. str. is homologous with the calyx or the corolla of taxa included inFagara, or of an independent origin, has been controversial for a long time, but the arguments mostly have remained theoretical. The present investigation of floral structures indicates that there are two different types of uniseriate perianth inZanthoxylum s. str. Therefore, this taxon does not represent a natural group and should be united withFagara asZanthoxylum s.l. The infrageneric taxonomy of this genus is still very ambiguous. It is shown that differences in indumentum, number of sepals and petals (5-4-3) resp. perianth segments (4–9), stamens (3–6), and free carpels (1–5) are of systematic relevance. Particularly important but so far neglected is carpel shape, where an acrostylous and an anacrostylous-basistylous type can be recognized. Stigmata of 2 or more carpels mostly fuse to form a compitum. 4–5-merous flowers with calyx and corolla, and acrostylous carpels are considered as plesiomorphic character states in the genus. On the basis of ± corresponding morphological and phytochemical progressions a working hypothesis about the relationships withinZanthoxylum s.l. is presented in graphical form (Fig. 9).Adapted from a lecture held at the 10th Symposion on Morphology, Anatomy, and Systematics in Göttingen, February 1991.     

Pollen evolution and systematics inAnnonaceae with special reference to the disulcate Australian endemic genera

All genera ofAnnonaceae endemic in Australia (Ancana, Fitzalania, Haplostichanthus) show almost exactly the same type of disulcate (disulculate) pollen with intact exine extending over the sulci. Tetrad stages inHaplostichanthus andAncana reveal a latudinal subequatiorial orientation of the two sulci at the proximal hemisphere. Sometimes they fuse into a ±zonosulcate aperture.Fissistigma pollen grains are ±globose and have a flattened pole with a central elevation and a concentric groove, covered by a somewhat reduced exine. This palynological characters give further support for separating the generaAncana andFissistigma. Germination was observed inHaplostichanthus where the pollen tube emerges at one of the two sulci and inFissistigma where the flattened part breaks up during germination. The aperture types described here are obviously transitional stages between aperturate and inaperturate pollen grains and are discussed in regard to pollen evolution.     

CARPELLARY VASCULATURE AND THE OVULAR VASCULAR SUPPLY IN DRIMYS

The ovules in Drimys winteri var. chilensis and D. lanceolata are consistently vascularized entirely by the ventral bundles, without contribution from the dorsal bundle(s) as generally assumed. The ovules are initiated in two rows, without any in “median” position. Post-initiatory differential growth of the carpel wall brings the lowermost ovules into apparently median position at maturity. The anomalous vascular supply to the lowermost ovules is thought to be related to concurrence of delayed initiation and development of these ovules with delayed differentiation of the vascular supply.     

ORGANOGENESIS IN THE CARPELLATE FLOWER OF DRIMYS LANCEOLATA

This study of floral development in Drimys lanceolata in Section Tasmannia provides a basis for comparison with D. winteri, a member of the section Wintera, which has been described previously. The carpellate flowers of D. lanceolata have 2 sepals, 4–6 petals, and a solitary carpel, which form in acropetal succession. In symmetry the flower and its apical meristem are bilateral rather than radial, as in the flower of Drimys winteri. The floral apex of D. lanceolata is zonate while that of D. winteri is organized as a mantle and core. Preceding carpel initiation the floral apex of D. lanceolata is narrowly wedge-shaped, while that of D. winteri is low-convex. The entire apex is utilized in carpel initiation in D. lanceolata, involving many subsurface cell divisions over the entire summit. No apical residuum remains, and the carpel is terminal. In this feature the contrast with D. winteri is particularly marked, since in the latter, carpels are initiated laterally around the floral apex, which c an be recognized as an apical residuum after all appendages have formed.     

Variation in structural gender in the hermaphrodite Helleborus foetidus (Ranunculaceae): within- and among-population patterns

In hermaphrodite plants, variations in structural gender (defined as the ratio between male and female gametes) may occur at different levels (among flowers, plants, and populations). In this study, we investigated variation in four traits influencing structural gender (number of carpels, ovules per carpel, stamens, and pollen grains per stamen) within and among six distant populations of the hermaphrodite perennial herb Helleborus foetidus (Ranunculaceae) in the Iberian Peninsula. Our results show that the four traits investigated varied significantly at all levels considered. Traits influencing the female sexual component (number of carpels and ovules per carpel) showed greater variation at the lowermost levels (within flower and plant) than traits influencing the male component, which in turn varied more markedly among populations. Number of carpels per flower and number of pollen grains per anther were the most important traits affecting between-plant variation in structural gender. There was no evidence of significant plant-level trade-offs or correlations between the various male and female traits, which covaried differently across populations. The observed between-population variation in structural gender of Helleborus foetidus can be explained as a consequence of differences in self-pollination levels related to a flowers mating environment.