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ABSTRACT: Since the 1800s, natural health products that contain hawthorn (Crataegus spp.) have been used in North America for the treatment of heart problems such as hypertension, angina, arrhythmia, and congestive heart failure. Traditionally, Native American tribes used hawthorn (Crataegus spp.) to treat gastrointestinal ailments and heart problems, and consumed the fruit as food. Hawthorn also has a long history of use in Europe and China for food, and in traditional medicine. Investigations of Crataegus spp. typically focus on the identification and quantification of flavonoids and anthocyanins, which have been shown to have pharmacological activity. The main flavonoids found in Crataegus spp. are hyperoside, vitexin, and additional glycosylated derivatives of these compounds. Reviewed herein are the botany, ethnobotany, and traditional use of hawthorn while focusing on the phytochemicals that have been reported in Crataegus species, and the variation in the described chemistry between individual species.
Phytochemistry 05/2012; 79:5-26. · 3.35 Impact Factor
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Nadia Talent
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ABSTRACT: Gametophytic apomixis, asexual reproduction involving megagametophytes, occurs in many flowering-plant families and as several variant mechanisms. Developmental destabilization of sexual reproduction as a result of hybridization and/or polyploidy appears to be a general trigger for its evolution, but the evidence is complicated by ploidy-level changes and hybridization occurring with facultative apomixis. The repeated origins of polyploid apomictic complexes in the palaeopolyploid Maloid Rosaceae suggest a new model of evolutionary transitions that may have wider applicability. Two conjectures are fundamental to this model: (1) that as previously suggested by Rutishauser, like many sexual flowering plants the polyploid apomicts require maternal-paternal balance in the second fertilization event that gives rise to the endosperm, and (2) that the observed variation in endosperm ploidy levels relates less to flexibility late in development than to the known variation in developmental origin of the megagametophyte between mechanisms loosely categorized as diplospory and apospory. The model suggests explanations for the relative frequencies of apospory and diplospory, and for the wide but incomplete associations of apospory with a pollination requirement (pseudogamy) and of diplospory with autonomous development of the endosperm. It is suggested that pollination from other taxa may provide some adaptive advantage to pseudogamous apospory.
Theory in Biosciences 04/2009; 128(2):121-38. · 0.98 Impact Factor
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ABSTRACT: Apomixis in Crataegus is primarily aposporous and requires pollination. The embryo sac is of the Polygonum type. A combination of meiotically unreduced embryo sacs with apparently reduced pollen would violate the usual requirement for a 2 : 1 ratio of maternal to paternal contributions to the endosperm. We therefore investigated the origin of endosperm in seeds of sexual diploids and apomictic polyploids of the sister genera Crataegus and Mespilus. Flow-cytometric DNA measurements from embryo and endosperm in mature seeds were converted to ploidy levels using leaf-tissue information. The diploids had triploid endosperm. In c. 60% of seed from polyploids, one sperm apparently contributes to the endosperm, while 25% or more may involve two sperm. Additional results suggest that trinucleate central cells also occur. Fertilization of meiotically unreduced eggs is indicated. The ratio of maternal to paternal contributions to the endosperm in these apomictic Crataegus is not constrained to 2 : 1. They thus resemble some Sorbus (Pyreae) and very distantly related Ranunculus (Ranunculaceae). It is suggested that Paspalum (Poaceae) may have similarly flexible endosperm ploidy levels.
New Phytologist 02/2007; 173(2):231-49. · 6.64 Impact Factor
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ABSTRACT: Hawthorns and medlars are closely related genera in Rosaceae subfamily Maloideae, whose taxonomy remains poorly understood. Gametophytic apomixis occurs in polyploids, and diploids are sexual out-crossers, so ploidy level is of great interest, but suitable material for chromosome counts is of limited availability each year. The promise of flow cytometry is that it permits rapid measurement of nuclear DNA amounts from most tissues, and ploidy level can be inferred if climatic and taxonomic differences do not interfere. Our DNA measurements cover most of the taxonomic series in Crataegus, adding cultivated and naturalized Eurasian plants to the many wild plants collected mainly from south-central Canada and the southeastern and northwestern United States. We found that some variation in DNA amount per genome copy distinguishes certain taxa, but ploidy-level estimates are at least as clear as the published chromosome counts, especially in the most common diploid–triploid–tetraploid range, and to the single published higher (hexaploid) chromosome count, we add evidence of pentaploids. By comparing ploidy evaluations to morphology, we hypothesize that both autopolyploidy and allopolyploidy contribute to the taxonomic complexity. We compared DNA amounts in Maloideae with those in Gillenia, a likely sister genus to the subfamily, which has a smaller chromosome number.Les aubépines et les nèfles sont des genres voisins de Rosaceae, de la sous famille des Maloideae, dont la taxonomie demeure mal comprise. L'apomixie gamétophytique survient chez les polyploïdes, et les diploïdes sont à croisements externes, de sorte que le degré de ploïdie est d'un grand intérêt, mais le matériel adéquat pour le décompte des chromosomes est d'accessibilité limitée chaque année. L'intérêt de la cytométrie en flux est qu'elle permet de mesurer rapidement les quantités d'ADN, à partir de la plupart des tissus, et qu'on peut en déduire le degré de ploïdie, si les différences climatiques et taxonomiques n'interfèrent pas. Les mesures d'ADN effectuées par les auteurs couvrent la majeure partie des séries taxonomiques chez les Crataegus, y incluent des plantes cultivées et naturalisées d'origine eurasienne, ainsi que plusieurs plantes sauvages, récoltées surtout dans le centre sud du Canada, et le sud est et le nord ouest des États-Unis. On constate qu'une certaine variation dans la quantité d'ADN par copie du génome distingue certains taxons, mais que les estimations du degré de ploïdie sont au moins aussi claires que les décomptes de chromosomes publiés, surtout dans la gamme la plus commune diploïde–triploïde–tétraploïde; les auteurs ajoutent à un unique compte de nombre chromosomique supérieur (hexaploïde), la preuve de pentaploïdie. En comparant les estimés de ploïdie avec la morphologie, les auteurs formulent l'hypothèse que l'autopolyploïdie et l'alloploïdie contribuent à la complexité taxonomique. Ils comparent les quantités d'ADN chez les Maloideae avec les Gillenia, un genre vraisemblablement voisin de la sous-famille, lequel possède un plus petit nombre de chromosomes.
Canadian Journal of Botany 09/2005; 83(10):1268-1304. · 1.40 Impact Factor
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ABSTRACT: Black-fruited hawthorns in North America comprise two taxonomic groups within the genus Crataegus, section Brevispinae and section Douglasianae. The first of these has recently been shown to be monospecific, consisting of the blue-berry haw, Crataegus brachyacantha Sarg. & Engelm., of Louisiana and Texas. Crataegus section Douglasianae, however, comprises several taxa in a single clade that is not closely related to section Brevispinae, and that is now one of the best-studied groups of hawthorns at least in North America. Most taxa in the group are found in, or west of, the Rocky Mountains. They include diploids, triploids, and tetraploids that can be ascribed to four or more species that differ in distribution and ecology, thorn morphology, leaf shape, and floral architecture. Diploids are self-incompatible, whereas polyploidy is associ-ated with pseudogamous, gametophytic apomixis and self compatibility. Molecular data suggest that polyploids have arisen repeatedly, both within and from crosses between ploidy levels. We suggest that Crataegus section Douglasianae represents at least two agamic complexes that may serve as models for understanding the biology of, the relationships within, and the appropriate taxonomic treatment of other such groups that may make up much of the rest of the genus. Résumé : Les aubépines à fruits noirs de l'Amérique du Nord comportent deux groupes taxonomiques dans le genre Cratae-gus, la section Brevispinae et la section Douglasianae. On a récemment montré la nature monospécifique de la première sec-tion constituée de la cenelle à fruits bleus, Crataegus brachyacantha Sarg. & Engelm., de la Louisiane et du Texas. Cependant, les Crataegus de la section Douglasianae comprennent plusieurs taxons appartenant à un même clade qui est faiblement relié à la section Brachyacanthae, et qui constitue maintenant un des groupes d'aubépines les mieux étudiés, du moins en Amérique du Nord. On retrouve la majorité des taxons du groupe dans ou à l'ouest des montagnes Rocheuses. Ils comportent des entités diplodes, triplodes et tétraplodes attribuables à au moins quatre espèces différentes par leur distribution et leur écologie, la morphologie des épines, la forme des feuilles et l'architecture florale. Les entités diplodes sont autoincompatibles alors que les polyplodes, montrant de la pseudogamie et de l'apomixie gamétophytique, sont autocompatibles. Les données moléculai-res suggèrent que les entités polyplodes sont apparues de façons répétées à la fois par croisements à l'intérieur et entre degrés de plodies. Les auteurs proposent que la section Douglasianae des Crataegus représente au moins deux complexes agames qui peuvent servir de modèles pour comprendre la biologie des relations internes et le traitement taxonomique approprié d'autres groupes similaires qui pourraient fort bien constituer la majorité des genres résiduels du reste du genre.
