Effects of apomixis and polyploidy on diversification and geographic distribution in Amelanchier (Rosaceae).

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Premise Of The Study: Amelanchier polyploid apomicts differ from sexual diploids in their more complex diversification, greater species problems, and geographic distribution. To understand these differences, we investigated the occurrence of polyploidy and frequency of apomixis. This research helps clarify species delimitation in an evolutionarily complex genus.

Crataegus ×ninae-celottiae and C. ×cogswellii (Rosaceae, Maleae), two spontaneously formed intersectional nothospecies.

Crataegus monogyna Jacq. is naturalized in North America, where it has hybridized with native diploid hawthorns at least twice. We provide names for the two nothospecies (as well as for the corresponding nothosections and nothoseries), referring to existing documentation in the literature for nothosp.

A review of the chemistry of the genus Crataegus.

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.

Evolution of gametophytic apomixis in flowering plants: an alternative model from Maloid Rosaceae.

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.

Endosperm formation in aposporous Crataegus (Rosaceae, Spiraeoideae, tribe Pyreae): parallels to Ranunculaceae and Poaceae.

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.