Uzi Plitmann

Revision of the plant geographical territories of Israel and Sinai

The phytogeographical territories of Israel and Sinai are revised using a large mass of species distribution data. With the help of chorotype frequencies for 25 km2 individual squares in Israel, territories were defined on the basis of the first two most frequent chorotypes. The similarity of boundaries in the resulting phytogeographical map with a physiognomic map suggests that the latter may be used in preliminary stages of the preparation of plant geographical maps.

POLLEN-PISTIL RELATIONSHIPS IN THE POLEMONIACEAE

The multitude of floral architectures within angiosperms are complex adaptations (or adaptive strategies) insuring the transfer of pollen from a plant to another of the same species, the subsequent growth of the pollen tube in the style, and the fertilization of the ovule. During the past decade, ecologists and evolutionists have learned much about floral structure in relation to biotic and abiotic dispersal agents of pollen, specifically how the shape and sizes of flower parts optimize pollen transport and deposition by various pollinators (Kugler, 1970; Frankel and Galun, 1977; Faegri and van der Pijl, 1979; Cruden and Miller-Ward, 1981). Much more attention has been given to floral syndromes in relation to pollinators than to the integrated evolution of floral components, even though it is apparent that if the system is to remain functional, most evolutionary alterations in one component must be compensated for by changes elsewhere. Studies on that aspect have been rather few (Galinat, 1961; Pandey, 1971; Lee, 1978; Cruden and Miller-Ward, 1981). Many plant families have undergone extensive radiation in pollination biology, and correspondingly in floral form and size. Some of the changes are in characteristics involved in pollinator attraction; others are in characteristics immediately involved in pollen presentation, transfer and receipt. The position of stigmas is a notable example in the latter category. In species which are bird-pollinated stigmas may be exserted, whereas in butterfly-pollinated relatives the stigmas may be deep within the corolla tube; in bee-pollinated relatives stigmas may be near the orifice of the corolla tube. The position of the stigma is determined by the length of the style. Although this position is pivotal in maximizing pollen receipt, the great diversity in style length (10-fold differences in many genera) receives relatively little attention. Similarly, pollen characteristics and diversity have been described at length with an emphasis either on their taxonomic value (Erdtman, 1969, 1970) or on their biochemistry and physiological function (Barbier, 1970; Heslop-Harrison, 1971, 1979; Stanley and Linskens, 1974; Muller, 1979). Given that pollen grains must send tubes through the style on their way to the ovule, we may ask whether differences in style length are accompanied by differences in some attribute of pollen, and whether changes in style length of necessity are accompanied by changes in pollen. In general, the germination of pollen and growth of the tube are conditioned by the components of the pollen grain, as by physiochemical processes involving stigma and style (Rosen, 1971; Stanley, 1971; de Nettancourt, 1977; Heslop-Harrison, 1978, 1979; Clarke et al., 1979). The pollen may contain carbohydrates and lipids in several forms, enzymes, membranes, and amino acids, all of which are essential for germination and growth; however, many of them are not synthesized during tube growth. Some nutrients, such as polysaccharides and amino acids, can be absorbed from the style, whereas some other materials (especially m-RNA) cannot be obtained this way and thus function as limiting factors (Barbier, 1970; Mascarenhas, 1971, 1975; Stanley, 1971; Vasil, 1974). Since many similar provisions for growth must be present in the pollen grain

Breeding systems in thePolemoniaceae

Pollen — ovule ratios and percentages of stigmatic pollen germination (SPG) were measured for over 160 taxa of thePolemoniaceae. When related to taxa with known breeding systems, it is found that low SPGs and high P:O ratios characterize xenogamous plants, high SPGs and low P:Os characterize autogamous plants. There is a significant negative correlation between P:O ratio and SPG in the whole family as well as in certain genera. Both measures can serve as reliable indicators of the breeding systems in taxa of thePolemoniaceae and can be measured in dried or living specimens. Accordingly, most polemons feature “mixed” breeding system, i.e. facultative xenogamy or facultative autogamy. Xenogamy is common among the tropical genera and in theLeptodactylon, Phlox andPolemonium. Autogamy is more frequent in the tribeGilieae (particularly inGilia) than in the other tribes. Annual taxa tend to be autogamous, showing on the average higher SPG and lower P:O ratio. The lepidopteran-pollinated group of species have a higher mean P:O ratio and lower mean SPG thus indicating that such plants are associated with crosspollination more than the others.

Chromosome polymorphism, hybridization and colonization in theVicia sativa group(Fabaceae)

Vicia sativa L. s. l. is presented as a variable complex consisting of 7 subspecies, including wild types, weedy races and cultivated derivatives. The group is characterized by: (a) Decreasing aneuploid (dysploid) chromosome series (2n = 14 12 10,); (b) wide variation in karyotypes; (c) pronounced weediness and colonization of disturbed habitats; (d) cohabitation of several forms; (e) intergradations between the main morphological types; (f) predominance of self-pollination; (g) lack of full sterility between the main chromosome types. Plants with different chromosome numbers or different karyotypes are loosely interconnected by occasional hybridization, particularly in disturbed habitats. Colonization appears to be associated with reticulate evolution and the recombination of previously separated gene pools. The wide karyotypic polymorphism characteristic for this complex is interpreted as a result of such relatively recent processes.

Chromosome divergence in the genus Cuscuta and its systematic implications

SUMMARYCuscuta L. plants are holoparasites with high chromosome divergence. Species representing the three subgenera of the genus were checked for their chromosome number, length and behaviour. Chromosome numbers range between 2n = 8 and 2n = 60, and their size, although roughly uniform within species, varies between 1–23μm. On the whole, size or number of Cuscuta chromosomes cannot be used as diagnostic criteria, except for very few species with unique numbers or sizes. Some associations between certain systematic entities and chromosome characters can be inferred. Species of the Old World of subgenus Cuscuta Engelm. are characterized by inverted meiosis and apparently by holocentric chromosomes, whereas species of the two other subgenera, subgenus Motiogyna Engelm. and subgenus Grammica Yuncker, undergo the regular process of meiosis and have monocentric chromosomes. The presence of holocentric chromosomes does not seem to be associated with their number.

SEED CHARACTERS AND TESTA TEXTURE IN SPECIES OF THE VICIEAE: THEIR TAXONOMIC SIGNIFICANCE

ABSTRACT Over 90 species (99 taxa) of the four principle genera of the Vicieae from the Near East were subjected to morphological and scanning electron microscopic (SEM) analyses. The species were grouped in 26 clusters according to their testa patterns. A key based on seed characteristics has been constructed, to be used by botanists and archeologists. It includes most species of Israel and its environs, several of which are either cultivated taxa or their ancestors. The testa patterns can be used as specific taxonomic criteria in certain cases, but only a few associations between the seed-character groups and the systematic entities have been found. Among the genera, Lathyrusseems to be the most diverse in seed coat patterns.

Holocentric chromosome behaviour inCuscuta (Cuscutaceae)

The present study demonstrates thatCuscuta babylonicaChoisy has holocentric chromosomes. Evidence for this phenomenon comes from three different observations. (1) Mitosis: During metaphase and anaphase the sister-chromatids are situated parallel to the equatorial plane with no sign of localized kinetochore activity. (2) Inverted meiosis in microsporocytes. (3) X-rayed microsporocytes, in which the numerous chromosome fragments do not show any lagging or formation of micronuclei. We assume that only one out of the three subgenera inCuscuta, namely subg.Cuscuta, has holocentric chromosomes, while the two other subgenera have monocentric chromosomes.

Pollen tube attrition as related to breeding systems inBrassicaceae

In order to estimate pollen tube attrition and to relate it to the breeding system, numbers of microgametophytes within the stigma and at the bottom of the style were scored in species of theBrassicaceae, 17 sporophytically self-incompatible, 11 predominant inbreeders, 4 facultative outcrossers. Attrition was evident in almost all species. The mean number of tubes at the bottom of the style, and mean number of stylar tubes per ovule were significantly lower in outbreeders. The degree of attrition, measured as “attrition rate” (the proportion of tubes in the stigma that do not reach the bottom of the style) was higher in outbreeders; it was positively correlated with the pollen : ovule ratios as estimates of the degree of outbreeding in the species involved. In outbreeders, sexual selection seems to be rather effective in inhibiting certain microgametophytic genotypes from reaching the ovules. Because of the low number of tubes per ovule in most cases, we assume that, in theBrassicaceae, female choice may be more effective in sexual selection and in ensuing pollen tube attrition.

Factors affecting the dominance of Silybum marianum L. (Asteraceae) in its specific habitats.

Summary The annual Mediterranean thistle Silybum marianum L. is a synanthropic plant (i.e. related to human habitats) common in Israel. It dominates waste places and ants’ nests, and is disseminated by wind and ants. The purpose of this study has been to find out some of the possible factors during the plant’s life cycle, which may affect its dominance in its specific habitats. Our results show that: (1) There is no obvious allelopathic effect of S. marianum on the germination of other plants; (2) Its germinability is relatively high and not affected by removal of the elaiosome; (3) Thistle plants around the nests and in waste places are fast growing, have significantly higher biomass and more and larger heads than thistles in surrounding herbaceous habitats; (4) Where the thistles were removed, total number of companion species and their biomass have increased. The success of S. marianum may be primarily due to its aggressive vegetative growth, causing depression of adjacent species. Its seed production, achene dispersal modes, and germinability partly enhance its dominance. Ants’ nests probably had been the primary habitats from which ruderal (nitrophilous) species, such as S. marianum , have invaded special man-made habitats.

THE ECOGEOGRAPHIC DISTRIBUTION OF BREEDING SYSTEMS IN THE CRUCIFERAE (BRASSICACEAE) OF ISRAEL

Eighty-six species of Cruciferae in Israel, from two ecologically different types of habitats, desert and Mediterranean, were screened for a possible association between their ecogeographic distribution and their breeding systems. The use of pollen: ovule ratio as a valid indicator for the breeding system was supported by a significant correlation between this ratio and autogamous fruit set in a sample of 28 species. The distribution of breeding systems is largely bimodal. Based on pollen:ovule ratios, 60% of the taxa studied are xenogamous; the remainder are self-compatible and largely autogamous. The percentage of selfers was larger in the desert than in the Mediterranean territory, yet the differences between the frequencies of the two breeding categories in the two ecogeographic territories are not statistically significant. Contrary to the expected, in secondary habitats xenogamous taxa are more frequent than autogamous ones.