摘要:

Some of the most conspicuous fruit and seed remains from the Middle Eocene Princeton chert locality (Allenby Formation) are assignable to the Araceae. Several thousand campylotropous, reniform, spiny seeds 2.5–3.2 mm long x 1.8–2.3 mm wide have been found dispersed in the chert. Two fruits, each with a single locule and at least eight ovules, show three distinct wall layers and appear to have been fleshy. The two layers of seed integument have pitted isodiametric sclereids aligned in radial rows, the outermost being thinner walled. Spines are borne in three rows on the dorsal seed surface while the ventral side is flattened. Idioblasts that probably contained raphides are present in the outer integument. Nucellar tissue is attached to the integument for most of its length and is well‐preserved in some seeds near the chalaza and in the large conical shaped area beneath the micropyle. Endosperm cells with dark contents and curved, linear, monocotyledonous embryos are present in some seeds. Sections of seeds of living araceous taxa of the subfamilies Monsteroideae (Epipremnum, Rhodospatha) and Lasioideae (Urospatha, Cyrtosperma) were made for comparison. The fossil seeds represent a new taxon most closely related toCyrtosperma, Keratosperma allenbyensisCevallos‐Ferriz et Stockey gen. et sp. nov., Family: Araceae, Subfamily: Lasioideae, Tribe: Lasieae. The Princeton remains are the oldest described seeds of this tribe known to date and add to our knowledge of the subtropical elements of the Princeton flora.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb08822.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Evolutionary theory predicts that species with small ranges and few individuals will exhibit low levels of genetic polymorphism. We investigated the population genetic structure of two locally endemic and two geographically widespread species ofAstragalus. To facilitate direct comparisons among these congeners, three populations of each species were sampled in a consistent manner and scored for allozyme polymorphisms at 12 loci. Genetic polymorphism was lower in restrictedA. linifoliusandA. osterhoutithan in widespreadA. pectinatus. However, the restricted species do exhibit a moderate level of isozyme variation, comparable to that of widespreadA. pattersoniand higher than has been detected in several other rare plant taxa. As measured by Wright'sFstatistics, there were no consistent differences between the restricted and widespread taxa with respect to the organization of genetic variation. FSTvalues were low in all taxa, indicating little heterogeneity among populations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb08823.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

A fossil fern described originally by W. Fontaine asAspidium heterophyllumhas been reexamined. Based upon characteristics of the sorus, indusium, sporangium, and spores the plant belongs to the family Matoniaceae. There is no genus within the family to which the fossil can be assigned; thus, a new genus (Delosorus) is proposed. This report increases the number of plants within the Lower Cretaceous Potomac Group that belong in the Matoniaceae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb08824.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Chromosome numbers are reported for 20 collections of Hawaiian Lobelioideae (Campanulaceae), representing six genera, 13 species, and two interspecific hybrids. All aren= 14. Chromosome numbers are reported for the first time for eight species ofClermontia, Cyanea, Delissea, Lobelia, andTrematolobelia;the report forDelisseais the first for that genus. Additional determinations confirmed previously reported numbers in five other species ofBrighamia, Clermontia, andCyanea.Chromosome numbers are now known for all seven genera and 20 of the 110 species. All accepted counts aren= 14. It is suggested that all Hawaiian Lobelioideae share this number and are paleotetraploid. There is no evidence that the prolific speciation evident among these plants was accompanied by euploid or aneuploid change in chromosome number. The Hawaiian Lobelioideae, particularly the monophyletic lineage of 91 baccate species, offer further support for the generalization that change in chromosome number is an uncommon mode of speciation in insular floras.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb08825.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Experimental studies of the evolutionary biology of lichen fungi have been hampered by massive difficulties of in vitro culture and artificial crosses are still not possible. Gene flow in these organisms is demonstrated here for the first time by the analysis of secondary products in the progeny of individuals from natural populations of mixed chemotypes of theCladonia chlorophaeacomplex. All of the chemotypes in this study have been interpreted as distinct sibling species. In the Appalachian Mountains of North Carolina, however, thegrayiandmerochlorophaeachemotypes are found to belong to a single interbreeding populations that is reproductively isolated from thecryptochlorophaeachemotype. In the Coastal Plain, thecryptochlorophaeachemotype hybridizes with the local endemicperlomerachemotype. This study has major impact for species concept in lichens because consideration of neither morphologial tendencies nor biogenetic relationships of the secondary products could have predicted its result.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb08826.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

The effect of self pollen on the success of cross pollinations was studied inCampsis radicans(L.) Seem., a species previously considered self‐sterile. The application of self pollen to stigmas in combination with or preceding the application of cross pollen markedly reduced the likelihood of fruit production. This effect was not due to the dilution of cross pollen nor to physical blocking of the stigmatic surface, since mixtures of talc and cross pollen were as effective as pure cross pollen in causing fruit production. Pollen tubes produced by self pollen grew at rates similar to those from cross pollen, and penetrated the ovary. The interference caused by self pollen appears to take place in the ovary, although it cannot be stated to what degree it is prezygotic or postzygotic. The marked protandry occurring inC. radicansis presumed to be due at least partly to selection for avoidance of these negative effects on female reproductive success. Up to 33% of viable seeds from mixed self + cross pollinations were sired by self pollen. The term “cryptic self‐fertility” is coined to describe this phenomenon where pollination with loads of pure self pollen rarely or never yields fruit, but pollination using mixtures of self and cross pollen yields fruit containing considerable numbers of selfed seed. Estimates of selfing frequency that are based on pollination using loads of purely self pollen will be in error for species possessing cryptic self‐fertility.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb08827.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

The genusRqfflesiaincludes about 13 species of parasitic flowering plants, among which are the largest known flowers. The flower with subtending scales is the only part of the plant external to the host and is produced solitary on roots (rarely stems) of the genusTetrastigma(Vitaceae). Field studies were made of the pollination process inR. pricei, a species endemic to the Crocker Range in the Malaysian state of Sabah (northern Borneo). Pollination is mediated by carrion (bluebottle) flies of the generaLucillaandChrysomya.Experimental data indicate that both visual and olfactory cues are important in attracting flies to flowers. Flies (mostly femaleL. papuensis) obtain loads of the viscous liquid pollen matrix by visiting male flowers and entering anther grooves on the central column of the flower, precisely guided by ridges armed with hairs that force the fly into a position in which the pollen is positioned on the dorsal part of the thorax. “Windows” on the inside of the perigone diaphragm apparently help orient their flight inside flowers. Pollen‐loaded flies visiting female flowers may enter the infradiscoidal sulcus formed by a broad ring of stigmatic tissue above and the expanded base of the column below. On entering the sulcus the fly is wedged in so tightly that pollen is rubbed off the thorax onto the stigma. Only large flies could be effective in picking up pollen from male flowers and transferring it to female flowers. The pollination syndrome is sapromyophily, in which the flower closely parallels trap flowers of several other plant families, although it is not a trap. The flower provides no reward for pollinators but deceives them by an apparent offering of food and possibly brood place.Rafflesiaplants are extremely rare, perhaps in part because of infrequency of pollination, which requires neighboring male and female flowers simultaneously in bloom.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb08828.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Two years of water and nitrogen augmentation experiments onLarrea tridentata(creosote bush) were carried out in a southern Californian warm desert wash plant community. Treatments consisted of control (C), water (W), water and soil nitrogen (W + SN), and soil nitrogen (SN). Quantitative phenological data and microclimatic measurements were collected prior to the onset of and during the growth period and treatments. Predawn and midday water potentials were lower in nonirrigated than irrigated individuals. Leaf conductance was higher in irrigated than in nonirrigated shrubs, with a maximum difference of 1 cm s‐1observed in July 1984 under relatively low vapor pressure deficit conditions. Leaf production rates were significantly higher in the irrigated (W and W + SN) treatments than in the nonirrigated (C and SN) treatments in 1984. Addition of soil nitrogen caused no increased in vegetative growth rates in 1984. In 1985, a drier year, there was only minimal growth during the spring and summer growth periods in the nonirrigated treatments, while the W and W + SN treatments resulted in significantly higher leafand shoot growth rates. Growth rates in 1985 were significantly higher in the W + SN treatment than in the W treatment. Reproductive growth was higher in the nonirrigated than the irrigated treatments, with the lowest reproductive activity noted in the W treatment.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb08829.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

The hypothesis that outcrossers are competitively superior to close relatives with specialized genetic systems was tested. Interspecific competition between three closely relatedOenotheraspecies was examined in common garden environments.Oenothera grandis, an obligate outcrosser, is competitively superior to its derivative,O. laciniata, an obligate chromosomal heterozygote. Both of these species are superior toO. mexicana, a closely related facultative selfer. These relationships were consistent over two levels of density stress. Therefore, in this species triad, the outcrosser has a competitive advantage over its close relatives with derived breeding systems.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb08830.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Growth, biomass, and survival of bald cypress (Taxodium distichum[L.] Richard), water tupelo (Nyssa aquaticaL.), black willow (Salix nigraMarshall), and button bush (Cephalanthus occidentalisL.) were examined in a 3 times 3 factorial experiment varying water temperatures (AMBIENT, MID, and HIGH [~40 C]) and water levels (DRAINED, SATURATED, and FLOODED). Stem diameter and height, biomass, and survivorship for water tupelo and bald cypress were all reduced by the HIGH/FLOODED treatment. Black willow growth had the greatest variability among nonlethal flooding and temperature treatments, and achieved the greatest biomass of the four species. In the HIGH/FLOODED treatment, however, only 47% of the black willow seedlings survived and stem diameter, height, and biomass of survivors were greatly reduced. Button bush had intermediate variability of growth to the nonlethal treatments as compared to the other study species. Survival of button bush seedlings in the HIGH/FLOODED treatment was high (87%), but root biomass of the survivors was reduced. Interspecific differences in growth, biomass, survivorship, and morphological characteristics existed among these swamp species to experimental conditions. These responses may help explain vegetation patterns in a thermally impacted swamp.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb08831.x

出版商:Wiley    

年代:1988

数据来源: WILEY