Influence of achene heteromorphism on life-cycle traits in the annual weed gallant soldier (Galinsoga parviflora Cav.)

Galinsoga parviflora (gallant soldier), Asteraceae, produces two morphologically distinct achenes in a single capitulum: peripheral and central. The morphological, phenological and generative reproduction traits of the progeny derived from peripheral and central achenes that were cultivated in greenhouse conditions were analyzed. Differences between the progeny of various morph types were manifested at different stages of life. The plants of both morph types developed at a similar rate and they entered key phenological phases at the same time except for the flowering stage. The average height of the studied plants was similar on the same days of the experiment. The study showed that plants from peripheral achenes realize the generative reproduction in other pattern than plants from central achenes. The plants from central achenes produce more capitula per plant at the beginning of the fruiting stage, whereas plants from peripheral seeds achieve the highest number of capitula per plant at later stages. Finally, on day 130 of the experiment, the number of capitula per plant of both morphs equalized. At the early fruiting stage, the number of achenes per capitulum of plants from the two morphs did not differ significantly. The number of achenes within one capitulum decreases with plant age in both populations, but the rate of that decline is greater in the progeny of peripheral seeds. The number of peripheral achenes per capitulum in plants from both achene types decreases at a comparable rate. In contrast, the number of central achenes is reduced at a faster rate in plants germinated from peripheral achenes. After day 83, the individuals from peripheral diaspores intensified their reproductive effort; they produced more capitula but with fewer number of achenes than in individuals from central diaspores. On day 130, the number of dispores per plant of the two morphs equalized. The changes of fecundity of peripheral and central progeny with the age of the plant (at different stages of the life cycle of a single plant) contribute to an intensive seed rain throughout the fruiting period. By producing a large number of less fertile capitula with a stable number of peripheral achenes, plants derived from peripheral achenes are able to supply a higher share of peripheral achenes than if they would produce fewer but more fertile capitula. This strategy increases the pool of peripheral achenes.     

Differential outcrossing rates in dispersing and non-dispersing achenes in the heterocarpic plant Crepis sancta (Asteraceae)

The association between mating systems and dispersal in plants has been studied mostly in cleistogamous species where, generally, seeds produced by cleistogamous (selfed) flowers are less dispersed than seeds produced by chasmogamous (potentially outcrossed) flowers. In heterocarpic Asteraceae, non-dispersing fruits (achenes) are produced at the periphery of the capitulum (outer florets) whereas dispersing achenes are produced by inner florets in the same capitulum. Since all the florets are protandrous, the outer floret developing first are in female phasis when anthesis of inner florets takes place. Thus, outer florets can be potentially selfed by the inner florets of the same capitulum whereas the latter must be pollinated by flowers of other capitula. Therefore outer florets should be more inbred than inner florets. To test this hypothesis, we measured the natural outcrossing rate in outer and inner florets using allozymes in three populations of the heterocarpic Crepis sancta. The results showed that the outcrossing rate was highest for non-dispersed achenes. Moreover, among the outcrossed achenes within a capitulum it was observed that the number of paternal parents of non-dispersing achenes was higher than for dispersing achenes. The pattern observed was therefore the opposite to the pattern of cleistogamous plants and contradicts the putative pollination mechanism we proposed for Asteraceae. The results agree with the predictions of sib competition theory which considers that outcrossing may minimize competitive interactions among relatives (sibs) falling near the mother plant. Higher outcrossing rate in outer florets could also occur because pollinators are more attracted to these florets.     

Relationship between capitulum size and pre-dispersal seed predation by insect larvae in common Asteraceae

The evolution of a showy floral display as an advertisement to pollinators could simultaneously advertise the availability of resources to pre-dispersal seed-predators. The hypotheses tested here are that the incidence of seed predation by bud-infesting insect larvae in capitula of Asteraceae is positively related to (1) capitulum size among species, (2) capitulum size within species, (3) capitulum lifespan, and (4) the degree of flowering asynchrony on individual plants. Three populations of each of 20 common herbaceous species of Asteraceae from disturbed ground and grassland habitats were monitored for the presence of pre-dispersal, seed-eating insect larvae. Mean capitulum size (receptacle width) of each species was measured. In a sub-set of eight species, individual capitula were tagged to determine their flowering phenology and lifespan (from anthesis to seed shedding). From these data an index of flowering synchrony on individual plants was derived. Among species, the incidence of larval infestation increased with capitulum size. Small-flowered species such as Achillea millefolium were largely free of bud-infesting larvae, whilst large-flowered species such as Arctium minus were heavily infested. In three cases investigated in greater detail, bud infestation was found to increase with capitulum size within species, suggesting a potential for natural selection to favour smaller capitula. No relationship was found between infestation levels and either capitulum lifespan or degree of flowering synchrony, and there was no evidence that the relationship between capitulum size and infestation was confounded by correlations with these other features. The results support hypotheses 1 and 2, but not 3 and 4. It is suggested that the characteristic capitulum size of each species may represent a trade-off between the opposing selection pressures of pollinators and pre-dispersal seed predators.     

Oviposition choice by the Onopordum capitulum weevil Larinus latus (Coleoptera: Curculionidae) and its effect on the survival of immature stages

Female Larinus latus lay eggs into the capitula of their Onopordum spp. host plants from the onset of capitulum development until the completion of flowering. This tight linkage between insect life-history and plant development optimised larval survival, apart from some initial asynchrony between the readiness of the females to oviposit and the suitability of the very small capitula to physically support eggs. Eggs were laid on bracts and stems of capitula or directly in the florets, when these became available. Both the location of the egg and time of oviposition influenced mortality factors such as egg and larval parasitism, egg desiccation and larval establishment. Overall, survival of eggs laid later in the season into florets was higher, although the adults that emerged were smaller. The change in choice of oviposition site that occurs at the onset of flowering, not only favours survival, but ensures more efficient resource use by the larvae. This occurs because sequential flowering of Onopordum spp. drives a sequential oviposition pattern and spreads the egg load more evenly over the available capitula, reversing a trend earlier in the season to clump eggs that were laid directly on the bracts. Other potential constraints, such as capitulum size, absolute egg density and previous egg-laying do not play a major role in determining the oviposition pattern of L. latus. Larval survival was positively correlated with capitulum size and not strongly influenced by egg density. Competition for resources only appeared to play a role in smaller capitula, and manifested itself in a reduction in the size of emerging adults rather than the death of immatures. In the absence of strong interspecific competition, the oviposition behavior of L. latus has become geared to maximising resource use for larvae (i.e. its own potential competitiveness) rather than minimising interactions with other members of the capitulum endophage guild.     

VARIATION IN SEED WEIGHT AND ITS EFFECTS ON GERMINATION IN PASTINACA SATIVA L. (UMBELLIFERAE)

Pastinaca sativa (wild parsnip) produces seeds on the primary, secondary, and tertiary umbels of the flowering stalk. Within plants, variation in seed weight is about twofold. Secondary and tertiary seed weight is 73% and 50% of primary seed weight, respectively. Maximum variation in seed weight between plants is sixfold when tertiary seeds from a small plant are compared to primary seeds from a large plant. Within an umbel order, variation in seed weight between plants is correlated with plant size. Under autumn germinating conditions in the laboratory, final germination of seeds from different umbel orders does not differ but smaller seeds germinate more rapidly than larger seeds. Under spring germination conditions in the laboratory, significantly more primary and secondary seeds germinate than tertiary seeds and the rate of germination is independent of seed weight. Field germination of seeds from different umbel orders produces similar results except that in the spring both secondary and tertiary seed germination is lower than that of primary seeds. These results suggest that with respect to seed germination characteristics small seeds may have a competitive advantage over large seeds in the autumn because they germinate more quickly, but in the spring small seeds are at a disadvantage because they have lower overall germination. Because most germination in the field occurs in the spring, population recruitment from small seeds is likely to be substanially less than that from large seeds.     

Partial self‐incompatibility in the polyploid endemic species Scalesia affinis (Asteraceae) from the Galápagos: remnants of a self‐incompatibility system?

Different pollination treatments of capitula were used to examine the breeding system of individuals of the tetraploid endemic species Scalesia affinis from the Galápagos Islands. All types of crossings resulted in approximately 35 achenes per capitulum, but in actively and passively self-pollinated capitula these were mostly without embryos. Among self-pollinated individuals a large variation was found in the production of embryos. Some individuals failed completely to set filled achenes while others produced few or many. Additionally, we found a clear difference in female phenology of florets in self-pollinated capitula compared with florets in cross-pollinated capitula. Female florets in self-pollinated capitula remained receptive for longer time. These results suggest that Scalesia affinis is partly self-incompatible. Outcrossing is assured by the endemic carpenter bee, Xylocopa darwini , which proved to be an important pollinator of Scalesia affinis . Nevertheless, geitonogamy seemed to be considerable in the focal population, for which reason open pollinated capitula produced fewer achenes than controlled outcrossed capitula.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 93–101.     

Origin and Development of Secondary Capitula in Calendula officinalis L. in Response to Gibberellic Acid

Foliar application of gibberellic acid greatly enhanced theformation of secondary capitula. The proportion of primary capitulashowing this feature increased from 6% in the controls to 28,58, and 54% at 100, 250, and 500 parts 10^–6 GA₃, respectively.Secondary capitula were initiated either along the peripheryor in the centre of the receptacle or from both; their totalnumbers for 15 plants per treatment were 53, 215, 660, and 404in response to 0, 100, 250, and 500 parts 10^–6 GA₃, respectively.Secondary capitula were smaller and had fewer disc florets andfruits, particularly of the ‘wingless and small’type. Tertiary capitula, not observed in nature, formed on 2.72and 3.21% of the secondary capitula on plants sprayed with 250and 500 parts 10^–6 GA₃.The formation of a secondary inflorescencemeristem in treated plants in place of a floret primordium canbe detected histologically early in its development, and itspattern of development resembles that of the primary capitulum.     

Phenological and morphological differentiation in annual Chaetanthera moenchioides (Asteraceae) over an aridity gradient

Flowering-time, plant longevity and size of capitulum were studied in a common garden experiment on seven populations of annual Chaetanthera moenchioides derived from a strong latitudinal aridity gradient in the mediterranean climate area of Chile. Populations derived from the drier northern part of the latitudinal gradient showed significantly shorter flowering and fruiting phenology and smaller capitula under uniform growing conditions. Water stress experiments performed in the greenhouse induced further phenological hastening and a reduction in number of ray florets per capitulum. Population differentiation and the reaction norms in C. moenchioides agree with the predictions of genetic-assimilation given that the plastic response of the species under water stress mimics phenotypic differentiation that has evolved along the environmental gradient.     

Reproductive traits associated with invasiveness in Conyza sumatrensis

Conyza sumatrensis (Retz.) E. Walker, a member of Asteraceae, is a highly invasive species. However, its reproduction biology remains poorly known. To understand the role of reproductive traits in successful invasion of the species, we studied several traits of its reproductive system: the miniature capitulum and gynomonoecious sexual system, the biology and phenology of capitula and florets, pollen/ovule ratio, the mating system (selfcompatibility), flower visitors, physical traits and dispersal potential of achenes, germination potential of achenes from manually pollinated capitula, and the association of these traits with invasiveness. Our study showed that the reproductive traits of autonomous seed production, versatile mating system of self- and cross-pollination, and generalized pollination system might contribute to the species' successful invasive capability. The invasiveness was further enhanced by the high and rapid production of achenes, as well as the high percentage, rapid germination rate and high dispersal capability of achenes. It was concluded that in annual or winter-annual weeds, autonomous seed production contributed significantly to the invasiveness of the species.     

The Relationship Between Achene Weight,Embryo Weight and Germination inTaraxacumApomicts

Apomicts provide the opportunity to investigate the variation in achene size and performance that is due to factors other than genetic differences between achenes. Achene characteristics of a single capitulum from each of 15 biotypes of apomicticTaraxacumwere investigated. Within a capitulum, achene fresh weight ranged from 4.45-fold to 13.74-fold. Overall, 59.8% of achenes germinated. The probability of any one achene germinating was influenced both by its source and by its weight and ranged from 0.049 to 0.902 between capitula and from 0.028 to 0.873 between weight classes. An investigation of the relationship between achene parts in three biotypes identified a linear trend for embryos to acquire a greater proportion of total achene weight as achene weight increases. Although the heaviest achenes showed the best germination, it is predicted that, for a given investment of maternal resources, seedling number would be maximized by producing achenes of a single intermediate weight.     

Ecological correlates of achene mass variation in Chrysothamnus nauseosus (Asteraceae)

Chrysothamnus nauseosus (Asteraceae) is a complex polymorphic shrub species widely distributed in western North America. In a study of 86 populations belonging to 15 subspecies, achene mass varied among populations over a sevenfold range. Achene mass was closely correlated with capitulum size at the subspecies level, varied little between wild-growing and common-garden-grown members of a population, and was under strong genetic control. Subspecies with the heaviest achenes are restricted to specialized edaphic environments (dunes and badlands) or late seral montane riparian communities, while subspecies that are widely distributed and that occur in early seral habitats have less heavy achenes. Selection on achene mass has apparently been a notable feature of the adaptive radiation of Chrysothamnus nauseosus into the wide array of habitats it currently occupies. Within a wild population, achene mass was greater for plants fruiting in midautumn than for plants fruiting early or late in the autumn, and this same trend was observed within individual plants in garden populations, indicating environmental control, perhaps through resource limitation. Highly significant between-plant differences in achene mass were found in both wild and garden populations, suggesting that within-population genetic variation is sufficient to permit continuing selection.     

Floret specialization, seed production and gender in Artemisia vulgaris L. (Asteraceae, Anthemideae)

Flowering and fruiting behaviour of female and hermaphrodite florets is described and assessed in samples from three populations from Denmark, England and Sweden. Between 25 and 50% of the florets in capitula are female, and flowering gender varies little among plants in each population. Fruiting gender of individuals, G (femaleness), varies from 0 to 0.85, because of variation in fruit set and fruit abortion. Variation in fruiting gender was correlated with plant size parameters in two populations, but not in the third. The data suggest that post-anthesis regulation of maternal investment may be operating. Florets of A. vulgaris are either totally specialized for pollen receipt (female florets) or largely specialized for pollen donation (hermaphrodite florets), and show adaptations for avoiding interference with each other in these functions. Movement of capitula from a pendent position at flowering to an erect position at fruiting optimizes positions for dissemination of pollen and of seeds respectively.     

Factors Contributing to Variation in Seed Production among Remnant Populations of the Endangered Daisy Gerbera aurantiaca1

The species‐rich mist‐belt grasslands of southern Africa have been severely reduced in extent as a result of commercial afforestation, thus confining many endemic plants and animals to small populations in habitat fragments. We investigated the influence of various environmental factors on seed production and seedling recruitment in remnant populations of the endangered grassland herb Gerbera aurantiaca (Asteraceae). Experiments with color traps showed that Eriesthis beetles, which appear to be the primary pollinators of G. aurantiaca, were most abundant in the two largest y extant populations. Seeds are produced in a very small proportion (typically <10%) of the ca 80 female florets in a capitulum. The mean number of seeds produced in undamaged capitula was found to be significantly lower in small than in large populations. Pollen limitation was evident from a significant overall increase in seed set after supplementalpollination in three populations over two seasons. The proportion of capitula containing seed predators did not differ markedly among populations or years, but lepidopteran larvae, which destroy all of the seeds in a capitulum, weremost abundant in the two largest populations in 2003. The presence of juvenile plants varied markedly amongpopulations, but this could not be linked firmly to estimates of seed production. Clonal growth is likely to contribute to the persistence of small isolated populations of G. aurantiaca, even when seed production is severely compromised by pollen limitation and predation.     

Modifiers of heterocarpy determine capitulum size inMicroseris hybrid D 14 (Asteraceae — Lactuceae)

The proportion of the outer, “hairy” achenes in capitula of hybrid D 14 (Microseris pygmaea × M. bigelovii) is determined by the same major gene as in its sister hybrid, B 87, as shown by marker segregation. Crossover between major gene and markers shows their genetic independence. Two modifiers segregating 9:7 influence the proportion of hairies in plants homozygous for the major gene. These same modifiers (or two genes linked with them) also determine the segregation of the number of achenes per head. Most likely, the modifiers act indirectly via a residual dependence of heterocarpy on capitulum size within strict quantitative limits set by the major gene. The identification of modifiers in a polygenic system as major genes for another character acting pleiotropically supports our contention that relatively few genes interact in plant development to determine key morphological characteristics at the organismic level.     

Ecology of achene dimorphism in Leontodon saxatilis

BACKGROUND [corrected] AND AIMS: Leontodon saxatilis produces two morphologically distinct achenes (morphs) in a single capitulum: one row of dark brown achenes without a pappus lies at the edge ('peripheral achenes'; 0.74 +/- 0.18 mg) while the inner ones are light brown with a pappus ('central achenes'; 0.38 +/- 0.07 mg). The hypothesis that achene heteromorphism in L. saxatilis widens its ecological amplitude was tested. KEY RESULTS: Achenes of both morphs germinated over the same range of temperatures (6-33 degrees C) but the central achenes showed significantly higher germination percentages, and the two also differed significantly in their annual dormancy cycle, with the peripheral achenes showing greater dormancy for part of the year. Seedlings from the two morphs did not differ significantly in total biomass after 2 and 4 weeks of growth, neither did they differ significantly in root and shoot weight and root:shoot ratio. Plants from both morphs growing at different regimes of soil moisture, nutrients and competition did not differ significantly in their number of achenes per capitulum. While the number of central achenes varied, that of peripheral achenes remained constant at approx. 13. Drier soil led to an increase in the number of central achenes in plants from both morphs. CONCLUSIONS: The peripheral achenes can replace the mother plant in the following growing season, whereas the central achenes are well adapted for wind dispersal and thus for colonization of new sites. However, the extent of variation in germination characteristics was similar to that found in seed populations of homomorphic plants, which suggests that germination percentage and other growth characteristics do not contribute to widening the ecological amplitude. The habitat of most heteromorphic species, the morphs of which differ greatly in germination and/or growth characteristic, are deserts or highly disturbed areas where such differences are highly advantageous, but in the moderate habitat of L. saxatilis the differences may prove a disadvantage.     

The effect of galls induced by the gall fly Procecidochares utilis on vegetative growth and reproductive potential of crofton weed, Ageratina adenophora

Reproductive potential and vegetative growth of Ageratina adenophora (Spreng.) K. & R. (crofton weed) were measured under ambient conditions to evaluate the efficacy of the gall fly, Procecidochares utilis Stone as a biocontrol agent for this weed. Galls induced by the fly resulted in the production of underdeveloped capitula and a reduction in the number of capitula and filled achenes per capitulum. Galling had no effect on subsequent germination of the seed produced. Where vegetative growth was concerned the effect of galling ranged from a temporary cessation of growth to death of stems above the gall. Although galling promoted production of side shoots, the dry mass of above-ground material was markedly reduced.     

Eustenopus villosus (Coleoptera: Curculionidae) Feeding of Herbicide-Resistant Yellow Starthistle (Centaurea solstitialis L.)

A population of yellow starthistle (Centaurea solstitialis L.) near Dayton, Washington developed herbicide resistance in response to repeated applications of picloram and other auxin-type herbicides. Laboratory and field experiments were conducted in 1998 to determine host acceptability and suitability of this herbicide-resistant yellow starthistle population to the biological control weevil Eustenopus villosus (Boheman) (Coleoptera: Curculionidae). In choice and no-choice feeding and oviposition experiments using excised buds, the weevil did not demonstrate a consistent preference for either herbicide-resistant (R) or -susceptible (S) yellow starthistle. When caged on buds of intact plants, the E. villosus feeding rate of 97% did not differ between R and S types. Host plant suitability, measured as larval damage and development to adult weevils, was equivalent in R and S types, with weevils maturing in 46% of the R and in 32% of the S capitula bearing oviposition scars. The number of viable achenes per capitulum was reduced by 87% due to larval feeding, with no difference between R and S types. Observations at the field site where resistance was found revealed oviposition scars on 78% of the late-bud-stage capitula on 23 June 1998 and 73% of the flowering and postflowering capitula on 15 August 1998. Selection for herbicide resistance has not created host incompatibility for E. villosus nor reduced the effectiveness of E. villosus as a biological control agent.     

A nodding capitulum enhances the reproductive success of Cremanthodium campanulatum (Asteraceae) at high elevations in the Sino–Himalayan Mountains

Background: Flower orientation is considered an evolutionary response to pollinators and abiotic factors. Several members of the genus Cremanthodium (Asteraceae) growing in alpine habitats in the Sino–Himalayas have conspicuously nodding capitula, the function of which is not understood.

Aims: We investigated the influences of nodding capitula on floral thermal conditions, pollinator visitation rate, pollen viability and achene production in Cremanthodium campanulatum.

Results: (1) the nodding capitulum did not modify internal thermal conditions, but the elongated involucral bracts could shelter pollen from UV-B radiation; (2) water and UV-B radiation seriously reduced the viability of pollen grains; (3) capitula artificially held erect set significantly fewer achenes than nodding ones; and (4) no pollinator preference was observed between capitula that were artificially held erect and natural nodding ones.

Conclusions: This study indicated that the nodding capitulum of C. campanulatum may protect pollen from being damaged by UV-B radiation, being washed away from the anther and stigma, and enable it to avoid rain damage during the wet monsoonal period. Our results suggest that nodding capitula in C. campanulatum possibly confer a selective advantage and may be driven by non-biological agents rather than pollinator attractors.     

黄帚橐吾花序结构的资源配置与环境的关系

 为了系统地了解黄帚橐吾(Ligularia virgaurea) 自然种群的繁殖对策,在其繁殖分配研究的基础上,通过统计不同部位头状花序的生物量投入,进一步分析了存在于总状花序内资源分配上的结构效应及其对不同生境条件的反应。结果表明：1）总状花序、不同部位头状花序在资源投入上受其栖息生境各种生态因子的影响而在不同生境和平均种群密度间存在着差异,并表现出一定的趋势;2）可代表个体水平的总状花序大小、头状花序大小、头状花序数量和头状花序平均重量等特征,都与种群密度呈现出程度不同的负相关关系,而总状花序内不同部位的头状花序大小则与种群密度变化无关;3）总状花序内的资源分配存在着位置依赖性,这种显著差异表现为顶部头状花序比基部和中部头状花序有较大的资源分配;4）总状花序顶部、中部和基部头状花序的资源分配与总状花序大小表现出极显著或显著的负相关关系。     

Revision of Lactuca L. and Two New Genera of Tribe Lactuceae (Compositae) on the Mainland of Asia (Cont.)

Having mixed extremely various patterns of achenes for a long time in the genus Lactuca L., especially showed in the classification of it on the mainland of Asia, Lactuca L., the primary unnatural genus, becomes more nuclear in its limit. The present paper makes a revision to attempt providing a clear cline between Lactuca L. and its relative genera. On my opinion, only plants, represented by Lactuca sativa L., which have ovoid capitulum during its fruiting, numerous (7-25), yellow ligular florets and longitudinal 1-10 ribs or striae on each side of achenes, acute into filiform beak at its apex, should be defined as Lactuca L. In view of the present concept of Lactuca L., another group of plants, embodied by Lactuca indica L., having its broadening, thin winged-margin of, 1-3 striae on each side of achenes, black, dorsi-ventral compressed, acute into thick and short beak at its apex, evidently, should not be placed into Lactuca L., but be regarded as genus, i.e. Pterocypsela Shih, gen. nov. Pterocypsela Shih distributes in Eastern and southern Asia, where Lactuca L. does not occur. In China there is all of species, seven species, of Pterocypsela Shih. They are P. raddeana (Maxim.) Shih, P. indica (L.) Shih, P. elata (Hemsl.) Shih P. lacciniata (Houtt.) Shih, P. triangulata (Maxim.) Shih, P. sonchus (Lévl.) Shih and P. formosana (Maxim.) Shih, But in Mediterranean regions and Middle and Western Asia mainly distributes Lactu ca L., in which there are only seven species from western China, Xijiang autonomic district. They are L. dolichophylla Kitam., L. sativa L., L. altaica Fisch. et Mey., L. serriola Torner, L. dissecta Don, L. auriculata DC. and L. undulata Ledb. With the combination of violet-purple ligular florets non-ovoid capitulum during its fruiting, a little thick achenes, acuminate into longer. or short beak at its apex and 4-6 ribs on each side of it, Mulgedium tataricum (L.) DC. is evidently different from Lactuca sativa L. with combination of ovoid capitulum during its fruiting, yellow ligular florets and compres sed achenes, acute into filiform beak at its apex. There seems to be no point in refusing Mu lgedium Cass. as a genus. Strictly speak, Mulgedium Cass. seems to be reminiscent of Para prenanthes Chang (see bellow) without beak at the apex of its achenes. In Hengduan moun tains and mountain range of Himalayas M. tataricum (L.) DC. discoveries its relative par tners. They are M. bracteatum (Mook. f. ex. C. B. Clarke) Shih, M. lessertianum (Wall. ex C. B. Clarke) DC., M. monocephalum (Chang) Shih, M. umbrosum (Dunn) Shih, M. meridionale Shih and M. polypodifolium (Franch.) Shih. Having broadering and thickening margin and 4-7 striae on each side of achenes, grey, dorsi-ventral compressed, truncate and beakless at its apex, Lactuca sibirica (L.) Benth. ex Maxim. (Sonchus sibiricus L.) is not only different from Lactuca sativa L. with the combination of yellow ligular florets and filiform beak at apex of its achenes, but also from the genus Mulgedium Cass. with beak at apex of its achenes. Therefore, Lagedium Sojak, established by J. Sojak (1961), should be restored. It should be point out that Lagedium Sojak is monotypic genus excluding Mulgedium tataricum (L.) DC. with beak at the apex of its achenes, non-marginated. Lagedium Sojak widely distributes in temperate and frigid zone ofvnorthern hemisphere. In our country, Lagedium sibiricum (L.) Sojak, sole species of the genus, restricts its northeast region. Paraprenanthes Chang, the new genus, established by Ch. Ch. Chang (1950) based on Lactuca sororia Miq. and Lactuca yunnanensis Franch. seems to be a distinct genus. This genus is characterized by 4-6 ribs on each side of achenes, black, fusiform, a little thick and beakless at its apex. Besides above-mentioned two species, assigned by Chang, in forest of tropic and subtropic zones on the mainland of Asia there are many species with same structure in achenes like L. sororia Miq. and L. yunnanensis Franch. The genus Paraprenanthes Chang seems to be reminiscants of Mulgedium Cass. and Lagedium Sojak, but differs from the former in its beakless achenes, from the later in its non-marginated achenes and 4-6 ribs on each side of it. In our country, there are all species of the genus known in the tropic and subtropic zones on the mainland of Asia. They are P. sororia (Miq.) Shih, P. yunnanensis (Franch.) Shih, P. longiloba Ling et Shih, sp. nov., P. heptontha Shih et D. J. Liou, sp. nov., P. prenanthoides (Hemsl.) Shih, P. pilipes (Migo) Shih, P. thirionii (Lévl.) Shih, P. sylvicola Shih., sp. nov., P. multiformis Shih, sp. nov., P. auriculiformis Shih, sp. nov. and P. sagittiformis Shih, sp. nov.