THE PROBLEM OF PLOIDY IN ECHEVERIA (CRASSULACEAE) II. TETRAPLOIDY IN E. SECUNDA

Every chromosome number from n = 12 to n =34 and also many higher numbers are known in one or more of the 130+ species of Echeveria, and the numerical boundary between diploids and tetraploids is not immediately apparent. Echeveria also is extraordinary for the number and diversity of hybrids that it can produce in cultivation, both within the genus and with species of several related genera. In 42 collections studied, the morphologically and cytologically variable E. secunda of central Mexico has n = 30-32, often with one or more B-chromosomes, and some quadrivalents are formed at meiosis in nearly every cell. Twenty-four hybrids of E. secunda, with 22 species or cytotypes considered diploids, resemble the former much more closely in appearance, and at meiosis 15-16 paired elements (bivalents and multivalents) are formed, never more, regardless of the number of chromosomes, 12 to 34, that were received from the other parent. It is concluded that the 15-16 paired elements in these hybrids are formed by the 30-32 chromosomes received from E. secunda, and that most chromosomes from the other parents occur as univalents, although usually a few associate with pairs from E. secunda to produce multivalents. Hybrids of E. secunda with 11 definitely tetraploid species having n = 34 to n = 68 are nicely intermediate in morphology between their parents, form mostly or entirely bivalents at meiosis, and most, probably all, including five intergeneric hybrids, are fertile. These observations are all consistent with the conclusion that E. secunda is an autotetraploid, even though no plants of the species having n = 15 or 16 have been found, and even though some other species of Echeveria having as many as 34 gametic chromosomes appear to be effectively diploid. Observations on pollen stainability and on second-generation hybrids are all compatible with this conclusion. The high chromosome numbers in many Mexican Crassulaceae that are now effectively diploid may have originated as polyploids that have become diploidized by mutation, loss, or suppression of duplicated chromosomes, segments, and genes. Hybrids of E. secunda, with three other species that appear to be tetraploids, have less regular meiosis, apparently because all of the chromosomes from the other parents do not regularly form pairs in the hybrids. These three species may represent intermediate stages in the processes of diploidization.     

CHROMOSOMES,HYBRIDS AND PLOIDY OF SEDUM CREMNOPHILA AND ECHEVERIA LINGUIFOLIA (CRASSULACEAE)

Sedum cremnophila and Echeveria linguifolia have generally been placed in different genera on the basis of their flowers—largely because the petals are spreading in one and erect in the other—and the genera have been placed in different subfamilies. However, they are very similar vegetatively and in their unusual inflorescence, their karyotypes are similar (n = 33), and they readily hybridize to produce fertile F₁ hybrids. Study of hybrids of these two species with numerous others leads to the conclusion that each of the two is effectively diploid, with a genome consisting of 33 chromosomes that are all different and that do not pair with each other. Therefore, the good chromosome pairing and the fertility of the hybrid between them are the result of close structural and genetic homology between the corresponding chromosomes of the two species. Taxonomic revision to reflect their very close relationship is desirable. Some other species of Sedum and Echeveria also may need to be reclassified.     

POLYPLOIDY,DYSPLOIDY, AND CHROMOSOME PAIRING IN ECHEVERIA (CRASSULACEAE) AND ITS HYBRIDS

The 140+ species of Echeveria have more than 50 gametic chromosome numbers, including every number from 12 through 34 and polyploids to n = ca. 260. With related genera, they comprise an immense comparium of 200+ species that have been interconnected in cultivation by hybrids. Some species with as many as 34 gametic chromosomes include none that can pair with each other, indicating that they are effectively diploid, but other species with fewer chromosomes test as tetraploids. Most diploid hybrids form multivalents, indicating that many translocations have rearranged segments of the chromosomes. Small, nonessential chromosomal remnants can be lost, lowering the number and suggesting that higher diploid numbers (n = 30–34) in the long dysploid series are older. These same numbers are basic to most other genera in the comparium (Pachyphytum, Graptopetalum, Sedum section Pachysedum), and many diploid intergeneric hybrids show very substantial chromosome pairing. Most polyploid hybrids here are fertile, even where the parents belong to different genera and have very different chromosome numbers. This seems possible only if corresponding chromosomes from a polyploid parent pair with each other preferentially, strong evidence for autopolyploidy. High diploid numbers here may represent old polyploids that have become diploidized by loss, mutation, or suppression of duplicate genes, but other evidence for this is lacking. Most species occur as small populations in unstable habitats in an area with a history of many rapid climatic and geological changes, presenting a model for rapid evolution.     

REPRODUCTIVE BIOLOGY,POLLEN AND SEED DISPERSAL,AND NEIGHBORHOOD SIZE IN THE HUMMINGBIRD-POLLINATED ECHEVERIA GIBBIFLORA (CRASSULACEAE)

Little is known about the reproductive biology of the Crassulaceae. We studied a population of Echeveria gibbiflora in the Pedregal de San Angel ecological preserve in Mexico City, Mexico. Each flower is open and producing nectar 7 to 8 days. On the days of maximum nectar production (flowers 4–6 days old) an average of 14.5 μl accumulates in a flower per day. The maximum rate of nectar production is between 0700 and 0900 hours. The average sugar concentration in the nectar is 43.7%. In a given flower, pollen is exposed and the stigmas are receptive at the same time. The average natural fruit-set and seed-set are 56.6% and 35.5%, respectively. The pollen-ovule ratio is 124, and the plants are fully self-compatible. The flowers are pollinated by only one species of hummingbird (Cynanthus latirostris) and are never visited by insects. Pollen movement is very limited (mean of pollinator flight distances = 0.72 m, mean distance fluorescent dyes = 0.92 m). Seed dispersion is by gravity and wind, and also is very limited (an average of 1.07 m). The total genetic neighborhood area is 15 m² to 17 m², producing a neighborhood effective population size (N_b) of 5.01 to 39.7 individuals. This is a very small N_b, indicating that genetic drift may be a dominant force in the evolution of this species.     

THE CHROMOSOMES OF PACHYPHYTUM (CRASSULACEAE)

Eleven of the 12 species of Pachyphytum, all that are available, have n = 31–33 standard chromosomes, or a multiple. Accessory chromosomes were found in some or all collections of four species; some cells of one plant have more than 50 of them. Accessory chromosomes often occur in groups at metaphase I, corresponding to their origin from one to several chromocenters of prophase I. Intraspecific polyploidy occurs within five species, with diploids to 12-ploids (n = ca. 186) in P. compactum and diploids to decaploids (n = ca. 160) in P. hookeri. Although the basic chromosome number is high, evidence from meiosis in certain hybrids shows that the basic 31–33 chromosomes are probably all different: they do not pair with each other and they do not duplicate each other. Polyploids, with 62 or more chromosomes, are probably autopolyploids: they form multivalents, and the chromosomes they contribute to hybrids pair with each other. Three different probable hybrids have been found in the wild, and more than 300 hybrids have been produced in cultivation.     

THE CHROMOSOMES OF THE SEMPERVIVOIDEAE (CRASSULACEAE)

Uhl , Charles H. (Cornell U., Ithaca, New York.) Chromosomes of the Sempervivoideae (Crassulaceae). Amer. Jour. Bot. 48(2): 114–123. Illus. 1961.—Chromosome numbers are reported for 207 collections representing 68 of the ca. 95 species in this subfamily. Basic numbers are 16, 17, 18, and 19 in Sempervivum, Section Sempervivum (10 species, with many tetraploids and one hexaploid); 19 in Sempervivum, Section Jovisbarba (5 species, all diploid); 15 in Aichryson (9 species, including 1 aneuploid, 1 tetraploid, and 1 aneutetraploid); and strictly 18 in Aeonium (31 species, including 4 wholly and 1 partly tetraploid), Greenovia (3 species, 1 partly tetraploid), and Monanthes (10 species, including 2 wholly and 1 partly tetraploid). The cytological evidence appears decisive in ranking several species of disputed generic position definitely with Aichryson rather than with Aeonium. Possible relationships between various Canarian genera and certain North African species often classed in Sedum are discussed briefly in the light of the scanty morphological and cytological evidence. It is suggested that both these groups may be descended from the same ancestors that were widespread in North Africa before the deserts developed.     

STUDIES OF VEGETATIVE COMPATIBILITY-INCOMPATIBILITY IN HIGHER PLANTS. I. A STRUCTURAL STUDY OF A COMPATIBLE AUTOGRAFT IN SEDUM TELEPHOIDES (CRASSULACEAE)

Initial adherence of the cut surfaces occurred by 24 hr after grafting and was correlated both with a pronounced dictyosome activity along the graft interface and with callus proliferation in both the stock and scion. A necrotic layer of one or two collapsed cells in thickness initially extended as a continuous barrier between the stock and scion, but the layer was fragmented by 2–3 days after grafting as the callus proliferation continued. Graft incision also induced a mild senescence in cells at the graft interface characterized by a reduced staining intensity of the cytoplasm, replacement of the large primary vacuole by numerous smaller vacuoles, and the occurrence of flocculent material throughout the cytoplasm. Starch accumulated during the first day after grafting but disappeared by 2–3 days after grafting. The cellular senescence never proceeded beyond an early, nonlethal stage, and cells along the graft interface completely recovered by 3 wk after grafting. Procambial differentiation occurred across the callus bridge by 10 days after grafting, and mature vascular continuity was established by 14 days. The results of this study are discussed relative to cellular recognition phenomena and to proposed mechanisms for plant graft compatibility-incompatibility.     

ANT-POLLINATION OF THE GRANITE OUTCROP ENDEMIC DIAMORPHA SMALLII (CRASSULACEAE)

Formica schaufussi, a medium-sized ant common throughout the Piedmont and Coastal Plain of the southeastern United States, has been observed in association with Diamorpha smallii, a self-incompatible annual endemic to granite outcrops in the Southeast, over a 6-yr period. Observations of ants collected on the flowers show large numbers of the sticky pollen grains adhering to hairs and indentations primarily on the thoraces of the ants. Though small native bees and flies are frequent and sometimes effective pollinators, it is highly unlikely that the monotypic genus Diamorpha coevolved with the introduced honeybee, as has been suggested. Characteristics indicative of an “ant-pollination syndrome” include occurrence in hot, dry habitats, a high density of very small plants bearing overlapping inflorescences at a uniform height, and low seed number, pollen volume, and nectar quantity.     

中国景天属一些种的订正

本文对国产景天属的6种植物进行了分类订正。归并了7种1亚种和2变种,同时对中国植物志中景天属存疑种Sedum phyllanthum Levl.et Vant.和S.subtile Miq.的范围及其分类地位进行了讨论。根据对S.hsinganicum Chu ex S.H.Fu的模式标本以及S.floriferum Praeger模式标本图和模式产地标本的研究,确认二者所具性状均在S.aizoon L.的性状变异范围内,故予归并。S.onychopetalumFrod.,S.grammophyllum Frod以及S.anhuiense S.H.Fu et X.W.Wang经研究均被作为S.lineareThunb.的异名处理。S.formosanum N.E.Br.在《中国植物志》中被并入S.alfredii Hance,现恢复为独立的种。此外还报道了一个中国新记录种S.hakonense Makino。     

DIPLOIDY IN DNA CONTENT IN VEGETATIVE CELLS OF CLOSTERIUM EHRENBERGII (CHLOROPHYTA)1

DNA content of the nucleus in the placoderm desmid, Closterium ehrenbergii Meneghini was measured throughout the life cycle by epifluorescence microspectrophotometry after DNA specific dye [4′,6-diamidino-2-phenylindol (DAPI)] staining. Postulating a mean DNA content of gamete nuclei as 1C, the nucleus of a newly divided vegetative cell was 2C. Most vegetative cells in the stage of exponential growth had a DNA content from 2C to 4C, while most in stationary phase, with the highest frequency of zygote formation, were 2C. They became pre-gametes (2C) upon mixing two heterothallic strains. Four gametes were made by a DNA reduction division of each pre-gamete cell. Therefore, there was a nonmeiotic DNA reduction stage by one half. During germination, the zygote underwent meiosis to produce two gones, each of which contained one surviving nucleus (large nucleus) and one degenerating nucleus (small nucleus). The DNA content of these four nuclei was 1C basically. The DNA of the surviving nucleus duplicated to 2C and further quadruplicated to 4C without cell or nuclear division. These two 4C gones had different cell morphology from ordinary vegetative cells. After the first cell division following meiosis, each gone produced two vegetative cells in which the DNA content became 2C to 4C again.     

GERMINATION ECOLOGY OF SEDUM PULCHELLUM MICHX. (CRASSULACEAE)

Factors controlling the timing of seed germination were investigated in the small succulent winter annual Sedum pulchellum Michx. (Crassulaceae) in its natural habitat on unshaded limestone outcrops in northcentral Kentucky. At maturity in early July the dormant seeds are not dispersed but are retained in the fruits on the standing dead plants until September and October. Many, but not all, of the seeds afterripen in the fruits during summer, and at the time of dispersal some of them are dormant and some are nondormant. Germination and annual population establishment occur in September and October from seed reserves that have been in the soil for one or more years and from seeds produced in the current year. Germination of nondormant seeds may be prevented in autumn by lack of the appropriate combination of environmental factors including light, temperature and soil moisture in the seed's microsite. The effect of low winter temperatures on ungerminated seeds in the population is to induce nondormant seeds into secondary dormancy and to prevent afterripening of dormant seeds. Thus, in spring all the seeds in the population's seed reserve are dormant. During spring and summer some of these seeds afterripen, and they germinate in autumn when, and if, germination requirements are fulfilled.     

PRIMARY STEM VASCULAR PATTERNS IN THREE SUBFAMILIES OF THE CRASSULACEAE

Primary stem vasculature was investigated in seven genera and 69 species of the Cotyledonoideae, Kalanchoideae and Sedoideae. Vascular patterns in whole cleared stems were determined by number of leaf traces per leaf, number of leaf-trace sympodia per stem, and connections between traces and sympodia. Four patterns were found in the Cotyledonoideae, eight in the Kalanchoideae and four in the Sedoideae. Similarities and differences among the patterns are discussed and possible phylogenetic trends are suggested. Changes in vasculature during ontogeny were observed in the Kalanchoideae and related to patterns found in mature stems. Many species in all three subfamilies reveal a relationship between phyllotaxy, number of sympodia per stem, and the intervals at which leaf traces are connected to each sympodium. Patterns of vasculature were found to support many of the intergeneric relationships suggested by other studies of this family.     

THE FEMALE GAMETOPHYTE OF THREE SPECIES OF GRINDELIA AND OF PRIONOPSIS CILIATA (COMPOSITAE)

In the four species studied, Grindelia stricta ssp. blakei, G. arizonica, G. lanceolata, and Prionopsis ciliata (Haplopappus ciliatus), the female gametophyte develops according to the Polygonum (normal) type from the chalazal megaspore of a row of four. In most cases only two antipodal cells are formed, the micropylar one originally containing two nuclei. The number of nuclei increases in both cells; one or both antipodal cells typically grow laterally into the integument, often extending to near the surface of the ovule. This resembles the condition previously reported in Grindelia squarrosa. Since the four species of Grindelia have similar antipodal outgrowths, such outgrowths may be considered typical for this genus. The fact that Prionopsis resembles Grindelia in regard to outgrowths from the antipodal cells and differs in this respect from typical Haplopappus helps to justify its separation from Haplopappus, and perhaps its suggested merger with Grindelia.     

CHROMOSOMES OF GRAPTOPETALUM AND THOMPSONELLA (CRASSULACEAE)

Chromosome numbers are reported for probably all 11 species of Graptopetalum (x = 30–35) and for both species of Thompsonella (x = 26). Plants of two species of Graptopetalum have gametic numbers from about 240–275, more than have been reported in any other seed plants. In hybrids the 30–35 chromosomes in the basic genome of Graptopetalum and likewise the 26 in Thompsonella apparently do not pair among themselves, and the genomes seem to be no more potent genetically than those of other species in their subfamily having as few as 12 chromosomes. Species with these gametic numbers are therefore considered to be diploid. On the other hand, in hybrids between a diploid and a plant with a very high chromosome number the phenotype of the latter predominates, and most of its chromosomes pair with each other. Many such hybrids are fertile. These facts suggest that the high polyploids arose by autoploidy rather than by alloploidy. Nevertheless, they may store heterozygosity at some gene loci and release it in various dosages and proportions each generation.     

悬铃木方翅网蝽在中国的首次发现

悬铃木方翅网蝽原产北美地区,首次在中国区系中发现.该种新入侵害虫在湖北武汉等城市危害三球悬铃木.介绍了方翅网蝽属和悬铃木方翅网蝽的鉴别特征、分布和为害情况.     

THE INFESTATION OF MYTILUS EDULIS LINNAEUS BY POLYDORA CILIATA (JOHNSTON) IN THE CONWY ESTUARY, NORTH WALES

The incidence of the shell-boring parasite Polydora ciliatain Mytilus edulis from the Conwy estuary, North Wales is described.Amongst mussels >40 mm in shell length both the occurrenceand abundance of P. ciliata increased steeply with host size.Infestation was highest amongst mussels near the mouth of theestuary where around 60–65% of the population was parasitized;no systematic relationship between the incidence of P. ciliataand tidal elevation was observed. Mussel condition was negativelycorrelated with the degree of infestation. Moderately and heavilyinfested mussels, however, never accounted for more than ca.10% of this population and the overall detrimental effects ofP. ciliata on growth and production is thus probably quite small.Whilst heavily infested mussels were evidently more vulnerableto predation, the shore crab, Carcinus maenas, selected smaller,non-infested mussels whenever these were available. No obviousrelationships were found between the presence of P. ciliataand the incidence of either pearls or pea crabs. (Received 14 January 1991; accepted 2 April 1991)     

香薷中的化学成分

从香[Eltholtzia ciliata(Thund.)Hyland]中分出14个化合物,用波谱和化学等方法确定为6-甲基三十三烷(Ⅰ),13-环己基二十六烷(Ⅱ),β-谷甾醇(Ⅲ),棕榈酸(Ⅳ_a),亚油酸(Ⅳ_b),亚麻酸(Ⅳ_c),熊果酸(Ⅴ),5-羟基-6、7-二甲氧基黄酮(Ⅵ),5-羟基-7、8-二甲氧基黄酮(Ⅶ),5、7-二羟基-4′-甲氧基黄酮(Ⅷ),5-羟基-7、4′-二甲氧基双氢黄酮醇(Ⅸ),β-谷甾醇-3-β-D-葡萄糖甙(Ⅹ),5-羟基-6-甲基-7-O-α-D-半乳吡喃糖双氢黄酮甙(Ⅺ),刺槐素-7-O-β-D-葡萄糖甙(Ⅻ)。其中化合物Ⅺ为新化合物,除(Ⅳ_b)和(Ⅳ_c)外,其余为首次从该属植物中得到。     

PLOIDY ANALYSIS OF THE TWO MOTILE FORMS OF CHRYSOCHROMULINA POLYLEPIS (PRYMNESIOPHYCEAE)1

In some cultures of the flagellate Chrysochromulina polylepis Manton et Parke, established from cells isolated from the massive bloom in Skagerrak and Kattegat in 1988, we observed, two motile cell types. They were termed authentic and alternate cells and differed with respect to scale morphology. To investigate whether or not the two cell forms were joined in a sexual life cycle, the relative DNA content per cell and relative size of cells of several clonal cultures of C. polylepis were determined by flow cytometry. Percentages of authentic and alternate cells in the cultures were estimated by transmission electron microscopy. Pure authentic cultures (α) contained cells with the lowest level of DNA and were termed haploid. Two pure alternate cultures (β) contained cells with double the DNA content of authentic cells and were termed diploid. Other pure alternate cultures contained haploid cells only, or both haploid and diploid cells. Three cell types were observed, each capable of vegetative propagation: authentic haploid, alternate haploid, and alternate diploid cells. Both the haploid and diploid alternate cells were larger than the haploid authentic cells. Cultures containing diploid cells appeared unstable: cell type ratio and ploidy ratio changed during the experiment where this cell type was present, particularly when grown in continuous light. In contrast, cultures with only haploid cells remained unchanged at all growth conditions tested. Light condition may influence cell type ratio and ploidy ratio. Our attempt to induce syngamy by mixing different authentic haploid clones did not result in mating. Assuming that the authentic and alternate cell types are of the same species, the life cycle of C. polylepis includes three flagellated scale-covered cell forms. Two of the cell types are haploid and may function as gametes, and the third is diploid, possibly being the result of syngamy.