Maritima Var Research Articles

Competitive ability, neopolyploid establishment and current distribution of a diploid–tetraploid plant complex

Polyploidy is a pervasive phenomenon in nature and has significantly contributed to the adaptive evolution of plants. The conditions necessary for the spread of neopolyploids in populations of the diploid progenitor are limited; however, the superior competitive ability of neopolyploids may promote its establishment. Here, we assess the contribution of polyploidisation to the divergence of plant traits affecting competitive response, which could explain the successful establishment and current geographic distribution of polyploids. We conducted an intraspecific competition experiment using diploids, neotetraploids and established tetraploids of Jasione maritima var. maritima to determine whether cytotypes differ in phenological, growth and physiological traits and competitive response. Cytotypes respond differently under different competition scenarios with implications for cytotype establishment and distribution. Competition impacted all cytotypes, but neotetraploids were least affected by competition, and the tetraploids were the most impacted. Thus, competitive advantage may have contributed to the displacement of diploid populations and colonisation of new areas by neotetraploids but might have been lost afterwards. Evolutionary changes after polyploidisation have also been detected, and tetraploids invested more in belowground biomass, suggesting that root development might also play a role in colonising southernmost locations. Interestingly, diploids and both tetraploids seem to have different life strategies, the first investing in growth while the latter investing in reserves for the next season. Overall, polyploidisation seems to provide immediate changes that confer an advantage under competition that, together with other factors, may have allowed the establishment of neotetraploids.

The impact of habitat loss on pollination services for a threatened dune endemic plant.

Habitat loss is currently a major threat to biodiversity, affecting species interactions, such as plant-pollinator interactions. This is particularly important in self-incompatible plants relying on pollinators to reproduce and sustain their populations. Here, we evaluated how habitat loss affects the pollination system, plant individual-pollinator species interaction network, and plant reproductive fitness of the self-incompatible Jasione maritima var. sabularia, a threatened taxon from dune systems. This plant is a pollinator generalist, visited by 108 species from distinct taxonomic groups. Results suggest that increasing habitat loss led to a significant decline in pollinator richness, increased pollen limitation, and a decrease in reproductive fitness of J. maritima var. sabularia. Visitation rate per individual did not significantly change with available area, indicating that the quality of pollen differed across populations. The topology of the network between J. maritima var. sabularia individuals and its pollinator species did not change, which may be attributed to the stability in the core of pollinator species. This suggests that the lower fitness of plants with increasing habitat degradation may be explained not only by the lower richness of peripheral pollinators but also by the genetic structure of the plant populations, as there is a possible higher transference of less quality pollen by pollinators, ultimately compromising the persistence of plant populations. Our study highlights the need of future studies to integrate the fine details provided by individual-level networks, which will increase our understanding of the pattern of species interactions and its consequences for the fitness of threatened plant populations.

Research in Boraginaceae: A new variety of Cryptantha maritima, Cryptantha pondii resurrected, and Johnstonella echinosepala transferred back to Cryptantha

A review of the species Cryptantha maritima (Boraginaceae) supports the continued recognition of the three varieties, these differing in corolla size, ovule and nutlet number, and calyx vestiture. Mapping of these taxa from verified specimens demonstrates some geographic trends, but also some overlap in ranges. In the process of our study, we discovered a new taxonomic entity. Cryptantha maritima var. vizcainensis is described as new. This variety is restricted to the Vizcaíno Desert of Baja California Sur, Mexico and should be considered rare, as it is known to date from only eleven collections. It differs from the other three varieties of the species in having a canescent, appressed-strigose stem vestiture lacking spreading trichomes, in having a relatively large corolla, and in having a fruit derived from two 1-ovuled ovary lobes, developing into two heteromorphic nutlets. We also discovered that the species Cryptantha pondii, previously treated as a synonym of C. patula, should be resurrected as a distinct taxon. Cryptantha pondii is restricted to the western Vizcaíno Desert and to Natividad Island of Baja California Sur. It is morphologically distinctive in having bracteate flowers, relatively large corollas, and four smooth nutlets heteromorphic by size. It is to date known from only three collections and should be considered extremely rare. We also reviewed the morphological and phylogenetic status of Johnstonella echinosepala. This taxon shows similarities to Cryptantha maritima and also exhibits some morphological discontinuity between Pacific and Gulf populations in Baja California Sur. Evidence from both morphological and phylogenetic studies supports the transfer of this species from the genus Johnstonella back to the genus Cryptantha. Finally, we propose that both C. pondii and C. echinosepala are likely close relatives of C. maritima, all of the “Maritimae clade,” a group distantly related to the main core of the genus Cryptantha. This study confirms the great importance of studying herbarium specimens in taxonomic research.

Different Patterns of Ecological Divergence Between Two Tetraploids and Their Diploid Counterpart in a Parapatric Linear Coastal Distribution Polyploid Complex.

Polyploidization is a widespread mechanism of evolutionary divergence in flowering plants. Ecological divergence of polyploid lineages has been proposed as a key process shaping the distribution of cytotypes in nature (niche shift hypothesis); however, evidence for the role of niche separation in replicated diploid-polyploid species pairs is still needed. This study aimed to assess the role of abiotic factors shaping current cytotype distributions. For that, we examined the distribution and environmental niches of two varieties recognized in diploid-tetraploid Jasione maritima across the species range and within a putative contact zone on the Iberian Peninsula. We counted chromosomes, screened for ploidy across Iberian Peninsula and characterized environmental requirements using niche modeling tools. We found that J. maritima var. maritima is composed by diploids with disjunct distribution in the west coast of France and northwest Iberian Peninsula, and by tetraploids in Iberian Peninsula, while var. sabularia is tetraploid. In the Iberian Peninsula, two parapatric contact zones along a linear coastal distribution were detected, one between diploid and tetraploid var. maritima, and the other between tetraploids of the two varieties. Environmental variables of diploid populations from France are distinct from those of southern diploid populations, which are more similar to tetraploids. In general, niche modeling results are congruent with the observed distribution patterns, although the results suggest a wider contact zone between varieties and cytotypes. Tetraploids of both varieties revealed different degrees of environmental divergence in comparison with their diploid counterpart. Tetraploid var. sabularia differed environmentally from diploids suggesting niche divergence. In contrast, tetraploid var. maritima overlapped with diploid environmental niche and currently occupies its entire predicted range, whereas diploids are restricted to northern areas of their suitable environment. Differences in ecological envelopes facilitate the recognition of functional units of biodiversity within polyploid groups, allowing the study of factors related to post-polyploidization divergence. Thus, whereas changes in environmental requirements may have allowed tetraploid var. sabularia to spread in habitats not favorable to diploids, other factors are involved with the distribution of diploid and tetraploid var. maritima.

Is selfing a reproductive assurance promoting polyploid establishment? Reduced fitness, leaky self-incompatibility and lower inbreeding depression in neotetraploids.

Newly formed polyploids face significant obstacles to persistence and population establishment because of fitness costs of intercytotype mating. Selfing provides the opportunity to escape mate limitation, enabling production of new individuals and increasing the likelihood of fixation of new polyploid lineages. Still, association between self-compatibility and polyploidy is not always clear. We compared self-incompatibility and inbreeding depression in neotetraploids and their diploid progenitor to explore the direct effects of whole genome duplications on self-incompatibility and the implications of ploidy-driven changes for polyploid establishment. Outcross and self-pollinations were performed in diploids and synthetic neotetraploids of Jasione maritima var. maritima, and reproductive success was measured through fruit and seed production and seed germination. Self- and outcross offspring were grown under controlled conditions, and plant performance was measured through several fitness parameters. Neotetraploids showed an overall lower performance than diploids. Reproductive success was negatively affected by selfing in both cytotypes. However, greater variation in the expression of self-incompatibility was observed in neotetraploids; additionally, developmental and physiological parameters were not affected by selfing on neotetraploids, with an overall similar fitness of outcrossed and selfed individuals, resulting in lower inbreeding depression indexes. Neotetraploids might have benefited from selfing at initial stages after their formation. Genome duplications resulted in leaky self-incompatibility, enabling the production of offspring under minority cytotype disadvantage with similar fitness as outcrossed offspring. Our results support theoretical assumptions that selfing might be important for neopolyploid establishment, although changes in self-incompatibility might not be abrupt.

Крупномасштабная геоботаническая карта Тузлинской косы и острова Тузла (Керченский пролив)

During an ecological expertise the vegetation of Tuzla Spit and Tuzla Island, located in the middle part of the Kerch Strait (Fig. 1), was studied. This area is unique in terms of biological diversity and a presence of rare species (Ermolaeva et al., 2018). The study is based on 150 geobotanical relevés. Field data, topographic maps, and high-resolution satellite images were used in the vegetation mapping. The total area of the study is 383 hectares. There are the following hierarchical levels in the legend to the vegetation map: types of vegetation and classes of associations. A mapping unit is an association described according to the Braun-Blanquet system (Braun-Blanquet, 1964). The highest divisions of the legend are the types of vegetation: aquatic, coastal-aquatic, halophytic, psammophytic, steppe; they are given according to the ecological-phytocoenotic classification. Within the types of vegetation, classes of associations are given according to the ecological-floristic classification. 26 main numbers of the legend display the vegetation cover on the map. Geobotanical map reflects the state of vegetation in 2015 (Fig. 2). The vegetation of the island is heterogeneous. Plant communities as narrow stripes replace each other depending on the degree of moisture, salinity and orography. The sea currents have a great influence on the vegetation. In the southern part of the Taman Bay, suspension flows are directed from the South to the North and round the island, which leads to the “washing-up” of the southeastern part of the island represented by shallow waters and estuaries. It is occupied mainly by halophytic vegetation, the main dominants of plant communities are Juncus maritimus, Phragmites australis, Puccinellia distans, Bassia hirsuta, Salicornia pe­rennans, S. prostrata, Suaeda salsa, Elaeagnus angustifolia, Elytrigia elongata, Tripolium vulgare. The northwestern part of the strait is occupied by the area of jet streams of suspensions coming from the North to the South from the Sea of Azov. This caused the accumulation of sand-shell material in the northern and northwestern parts of the island forming raised areas co­vered by psammophytic and steppe communities. The main dominant species here are Crambe maritima var. pontica, Cakile euxina, Eryngium maritimum, Lactuca tatarica, Salsola tragus, Leymus sabulosus, Artemisia arenaria, Gypsophila perfoliata. As a result of the transport crossing construction, the vegetation cover was heavily transformed. The vegetation map of Tuzla Spit and Island for 2019 shows the changes that have occurred — the drainage of the territory and the reduction of the vegetated area (Fig. 3). Distribution of weed species, in particular Ambrosia artemisiifolia, is noted. The remained vegetation in the southern part of the Tuzla Spit and the southern part of the Tuzla Island has a great nature conservation value; there are unique plant communities and rare plant species listed in the Red books of different ranks (Red..., 2007, 2008, 2015): Cakile euxina, Crambe maritime, Glaucium flavum, Euphorbia paralias, E. peplis, Eryngium mari­timum, Astrodaucus littoralis, Asparagus maritimus, Centaurea arenaria, Argusia sibirica, Astragalus varius, Verbascum pinnatifidum, Leymus racemosus subsp. sabulosus, Secale sylvestre. There is an obvious need to organize a specially protected natural area in these areas.

Resolving the Taxonomic Identity of Prunus maritima VAR. Gravesii (Rosaceae) Through Genotyping Analyses Using Microsatellite Loci

Abstract Graves' Beach Plum (Prunus maritima var. gravesii) has been notable for its unique morphological form since a single individual was first discovered on Esker Point in Groton, Connecticut and formally described in 1897. This original clone is now extinct in the wild and is presently kept in cultivation on the University of Connecticut campus, with no additional wild plants discovered in 120 years. It was distinguished morphologically based primarily on its distinctive orbicular leaves, which differ from the ovate leaves found in P. maritima var. maritima. Prior studies have shown few morphological differences between P. maritima var. gravesii and P. maritima var. maritima and full reproductive compatibility has been experimentally observed between the two taxa. However, the few unique characteristics of P. maritima var. gravesii merit further investigation to determine if it has unique molecular differences relative to var. maritima that might lead to the prioritization of conservation and possibl...

A new rare species of Agalinis (Orobanchaceae) from the coast of Veracruz, México

A new species of Agalinis from the state of Veracruz is herein described, illustrated and compared with A. flexicaulis, A. harperi, A. maritima var. grandiflora, and A. peduncularis. This new taxon was found in a single locality in the northern coast of Veracruz, Mexico, near to a mangrove-swamp. Given its highly restricted distribution, this species is considered as endemic, being critically endangered as a consequence of local urbanization.

The intricate nomenclatural questions around Plantago holosteum (Plantaginaceae)

A nomenclatural study on the names of the narrow-leaved plantains linked to Plantago holosteum is presented. The names P. carinata, P. gerardii, P. holosteum, P. maritima var. apennina, P. subulata sensu Wulfen, and P. wulfenii have been studied. The name P. holosteum is lectotypified on illustration by Bauhin & Cherler, P. wulfenii by Willdenow on a specimen preserved at B while P. maritima var. apennina was neotypified using a specimen deposited at RO. For P. holosteum, an accepted and widely used name both in the floristic and the vegetation literature of SE-Europe, an epitype is designated here. The name P. carinata was proposed by Mertens & Koch to replace P. subulata sensu Wulfen non L., but is illegitimate (ICN, Arts. 52.2, 53.1). Plantago gerardii Schult. is a later homonym of P. gerardii Pourr. (= P. argentea), and therefore also illegitimate (Art. 53.2). All the names investigated in this paper are placed in the synonymy of P. holosteum here (some of them only provisionally), except for Willdenow’s P. wulfenii which is considered a heterotypic synonym of P. maritima.

Taxonomic remarks on Scilla anthericoides Poir. (Asparagaceae, Scilloideae), a neglected species from Algeria

Scilla anthericoides is a neglected name traditionally considered as Urginea maritima var. anthericoides. Based on recent field observations of living plants completed by karyological analyses, we promote again this taxon at species rank, under the genus Charybdis. It differs from other species of Charybdis maritima aggregate by many characters of flowers, fruits, bulbs, leaves and by ploidy level. It is endemic to the regional hotspot Kabylias-Numidia-Kroumiria in north-eastern Algeria. It is a threatened species that has been assessed as vulnerable.

Nomenclatural notes and morphological observations on Malva subovata s.l. (Malvaceae)

Nomenclatural notes and morphological observations on Malva subovata sensu lato (Malvaceae) are discussed. The names Axolpha wigandii, L. africana by Cavanilles, L. africana by Miller, L. maritima, L. maritima var. purpurea, L. maritima var. trilobata, L. rupestris, and Lavatera subovata are lectotypified upon specimens preserved in the Herbaria BM, COI, G-DC, LY, MPU, and upon illustrations by Cavanilles and Gouan, while L. gallica, L. rotundifolia, and Olbia canescens are illegitimate names. Cavanilles’ L. africana, L. maritima, and A. wigandii are confirmed to be synonyms of L. subovata. Miller’s L. africana, a prevoiusly published homonym of Cavanilles’ L. africana, refers to another species. L. gallica, L. maritima var. purpurea, L. maritima var. trilobata, L. rotundifolia, and Olbia canescens are to be considered synonyms of L. subovata s.s. On the basis of morphological features and distribution areas, the current infraspecific classification of M. subovata s.l. (three subspecies) cannot be retained, and the better choice is the recognition of only two infraspecific taxa (subsp. subovata and subsp. bicolor), while the subsp. rupestris is to be treated as a synonym of the autonymic subspecies.

Chromosome numbers of 50 vascular plants in South Korea

Variation or constancy in the chromosome number within taxa of different categories have been proven to be important characters for taxonomic groupings. In order to expand the current knowledge on somatic chromosome numbers of South Korean vascular plants, chromosome counts were made for 50 species (38 genera of 17 families). The first chromosome information for Glaux maritima var. obtusifolia Fernald, Hemerocallis hakuunensis Nakai, Hylotelephium verticillatum (L.) H. Ohba, Orostachys iwarenge f. magnus Y.N. Lee, and Teucrium viscidum var. miquelianum (Maxim.) Hara is presented. New chromosome numbers compared with previous studies are also counted in Aconitum pseudolaeve Nakai, Securinega suffruticosa (Pall.) Rehder, and Tricyrtis macropoda Miq., respectively. In addition, Eupatorium japonicum Thunb. is proven to show polyploidy with tetra- and pentaploid. Among studied species, the diploids (66%) and tetraploids (24%) prevail.

Distribution of Rare Plants- Ulsan, Busan, Yangsan

A total of 15 rare plant species, including CR species of Abelia spathulata Siebold & Zucc., Tricularia yakusimensis Masam., Wikstroemia ganpi (Siebold & Zucc.) Maxim., EN species of Jeffersonia dubia (Maxim.) Benth. & Hook.f., Hololeion maximowiczii Kitam., Deutzia paniculata Nakai, VU species of Drosera rotundifolia L., Pogonia japonica Rchb.f., Euphorbia fauriei H. Lev. & Vaniot, LC species of Iris ensata var. spontanea (Makino) Nakai, Lysimachia coreana Nakai, Iris ensata var. spontanea (Makino) Nakai, Utricularia racemosa Wall. and DD species of Veronica pusanensis Y. Lee and Glaux maritima var. obtusifolia Fernald, were observed during the study conducted on the distribution of rare plant species in the Ulsan·Busan·Yangsan region. Of the 15 taxa, 3 were trees and 12 were herbs. 6 taxa (Tricularia yakusimensis Masam., Hololeion maximowiczii Kitam., Drosera rotundifolia L., Pogonia japonica Rchb.f., Iris ensata var. spontanea (Makino) Nakai, Utricularia racemosa Wall.) were those found in wetlands, 4 taxa (Wikstroemia ganpi (Siebold & Zucc.) Maxim., Jeffersonia dubia (Maxim.) Benth. & Hook.f., Lysimachia coreana Nakai, Iris ensata var. spontanea (Makino) Nakai) on mountain slopes, 3 taxa (Euphorbia fauriei H. Lev. & Vaniot, Veronica pusanensis Y. Lee, Glaux maritima var. obtusifolia Fernald) in the coastal region, and 2 taxa (Abelia spathulata Siebold & Zucc., Deutzia paniculata Nakai) in the valley area. In the case of rare plant species found in wetlands, there has been damage caused by coast elevation, forest road construction and farming, and in the case of other rare plant species, there has been damage caused by developments and other detrimental factors. Wikstroemia ganpi (Siebold & Zucc.) Maxim. and Veronica pusanensis Y. Lee are especially in need of protective measures, since their habitat is decreasing and they are being damaged via picking.

Distribution of five rare plants in Korea

The natural habitats and distribution of five rare plants were recently discovered in Korea. Salomonia oblongifolia DC., which grows in mountain wetlands, was found in Gijang-gun, Busan, Gokseong-gun, Jeollanamdo, and Shinan-gun, Jeollanam-do. Glaux maritima var. obtusifolia Fernald, which grows along the coast, was found in Yangyang-gun, Gangwon-do, Pohang-si, Gyeongsangbuk-do and Buk-gu, Ulsan. Tillaea aquatica L. and Limosella aquatica L., which was previously not known to be present in Korea, were discovered in Gijanggun, Busan for the first time. Apocynum lancifolium Russanov, which has a narrow distribution range in Korea, was also found in Samcheok-si, Gangwon-do, Ansan-si, Gyeonggi-do, Siheung-si, Gyeonggi-do, Jung-gu, Incheon, Yeongdeok-gun, Gyeongsangbuk-do and Shinan-gun, Jeollanam-do.

PHYLOGENY AND SPECIES RELATIONSHIPS IN JASIONE (CAMPANULACEAE) WITH EMPHASIS ON THE ‘MONTANA-COMPLEX’

The evolutionary relationships of several, mainly Iberian, Jasione taxa (Campanulaceae) were investigated using molecular data. A parsimony analysis of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA was partially successful in elucidating some interspecific alliances. One of the main clades included three morphologically rather disparate species from S Spain and Morocco which might indicate that these areas were refugia during the last glaciations. The fact that most of the other taxa fell in a large polytomy suggests a recent origin of these species. Amplified fragment length polymorphisms (AFLPs) were analysed for a larger sample set of two taxa from within the ITS polytomy to assess the partition of genetic variation between and within populations. All the British accessions named J. montana var. montana were found to be close to those so-named from Spain. However, individual accessions of J. montana var. montana from Argyll (Scotland), Devon (SW England) and the Shetland Islands proved to be genetically different from each other. This might suggest a low level of genetic diversification from a common progenitor due to a rapid northward migration. It is proposed that J. montana var. bracteosa and J. maritima var. sabularia merit recognition at higher rank. The possibility that J. montana vars gracilis and latifolia are mere repetitive segregants of J. montana var. montana is considered.

Submerged vascular plants and water chemistry in the coastal marsh Albufera de Mallorca (Balearic Islands)

Ten species of aquatic macrophytes have been analyzed for seven environmental variables by means of a significance test. A synthetic view has been obtained through a cluster analysis for species and a principal component analysis for 17 variables which form the multidimensional space where we project the species habitats. Myriophyllum spicatum L., Najas marina L., Potamogeton crispus L., Potamogeton pectinatus L. and Zannichellia pedunculata Reichenb. are widely distributed in the Albufera. Ceratophyllum submersum L. and Ruppia maritima L. var. brevirostris Ag. are considered stenoic. The tolerance of Ceratophyllum submersum to salts is significantly low and that of Ruppia cirrhosa (Petagna) Grande and Ruppia maritima var. brevirostris significantly high. Ceratophyllum submersum has a significantly negative distribution with regard to chlorophyll a and phosphate concentrations. Ceratophyllum demersum L. and C. submersum primarily occur in nitrate-rich waters whereas Ruppia cirrhosa primarily occurs in low nitrate waters.

Meristic and Organogenetic Variation in Ruppia occidentalis and R. maritima

Floral meristic and organogenetic variation was sampled in Ruppia occidentalis from an alkaline lake of the Nebraska Sandhills and in Ruppia maritima var. rostrata from a saline, non-Sandhills lake nearby. The androecium is meristically stable, always having two stamens, but the gynoecium is not. Seventy-two percent of the flowers of R. maritima had four carpels and the others had three, and in 80% of inflorescences the two flowers had the same number. In about one-third of inflorescences having dissimilar carpel numbers, the four-carpellate flower was uppermost. The number of carpels in each flower of R. occidentalis ranged from four to nine, averaging six, and in 57% of inflorescences both flowers had the same number; of those that did not, most had more in the lower than upper flower. Twenty-five percent of the flowers had four carpels, 8% had five, 35% had six, 15% had seven, 14% had eight, and 3% had nine. Ordered, dimerous, decussate organogenesis through the first four carpels followed the same pattern in both species, but carpels beyond four were alternate with the first four and the decussate pattern was broken. The stomatiferous dorsal lobe of each carpel produced persistent gas bubbles that probably aid flotation of the inflorescence and might function in trapping pollen as well. Only ephydrophilous pollination was observed in both species.

HOST SPECIFICITY AND SUITABILITY OF APION HOOKERI KIRBY (COLEOPTERA: CURCULIONIDAE), A CANDIDATE FOR THE BIOLOGICAL CONTROL OF SCENTLESS CHAMOMILE, MATRICARIA PERFORATA MÉRAT (ASTERACEAE), IN CANADA

AbstractScentless chamomile, Matricaria perforata Mérat [= Matricaria maritima var. agrestis (Knaf) Wilmot], is a widely distributed, rapidly spreading and aggressive weed, especially in the three Prairie Provinces. The seed-feeding weevil, Apion hookeri Kirby (Coleoptera: Curculionidae), is widespread and common in its native range in the Palaearctic. It occurs in such differing climates as the Mediterranean in northern Africa and the boreal climate of western Siberia. The weevil was screened for its host specificity. In the laboratory, females oviposited into the flowers of species in six genera of the tribe Anthemideae, and one species in the tribe Astereae. However, the larvae developed only in Matricaria species, and one adult emerged from stinking mayweed, Anthemis cotula L. In a choice test, ovipositing A. hookeri preferred scentless chamomile 93:1 over stinking mayweed. These results confirm host records in the European literature. It is concluded that A. hookeri is a host-specific and promising agent for the biological control of scentless chamomile.

The biology of Canadian weeds. 99. Matricaria perforata Mérat (Asteraceae)

Scentless chamomile, Matricaria perforata Mérat, (=M. maritima var. agrestis (Knaf) Wilmott), is an introduced weed having an annual to short-lived perennial life cycle. Two cytotype races are found in Canada with a distinctive geographic distribution. The tetraploid (2n = 36) is abundant in agricultural habitats of the Prairie region, whereas the diploid (2n = 18) is found mainly in ruderal habitats of the Atlantic region. Infestations are found in many annual and perennial crops, pastures, wasteland, lawns, gardens, roadsides, fence lines, and ditches. The plant reproduces entirely by seed, producing up to 1.8 million seeds m−2 in dense monospecific stands. A density of 25 annual plants m−2 can result in a 55% reduction in spring wheat yield under cool wet conditions. Shallow preseeding tillage in late autumn or early spring is an effective method of cultural control. Several herbicides are recommended for control of the weed in crop and noncrop areas. Scentless chamomile is considered a suitable candidate for biological control. Key words: Weed biology, scentless chamomile, Matricaria perforata, Matricaria inodora, Matricaria maritima var. agrestis, Tripleurosperum inodorum

On the germination of Ruppia taxa in western Europe

The germination of different Ruppia taxa, viz. Ruppia maritima L. var. maritima, Ruppia maritima var. longipes Hagström and Ruppia cirrhosa (Petagna) Grande, was studied in relation to chlorinity and temperature (under long-day conditions and in the dark, with and without a stratification period), desiccation and redox-potential. Seeds of R. maritima var. maritima germinated best in fresh water and at chlorinities up to 24%. The optimum germination temperature was 28°C. A stratification period of 2 months (4°C) resulted in an increase in germination at relatively low temperatures (16–20°C). The seeds proved to be very drought-resistant. Low redox-potentials (−300 mV) inhibited seed germination. Seedlings did not grow very well in fresh water. Mature plants grown from seeds that germinated at relatively low temperatures (16°C) produced flowers and fruits within a short period (± 8 weeks), whereas plants from seeds which germinated at relatively high temperatures (28°C) needed a very long time (at least 5 months) to produce flowers and fruits. The seeds of R. maritima var. longipes germinated best at relatively low temperatures (8°C). A few seeds of R. cirrhosa germinated occasionally under a variety of environmental conditions. The germination ecology of these taxa fits well within the circumstances that they are exposed to in their habitats in western Europe.