13 research outputs found

    New Species of Phoradendron (Viscaceae) from Mexico and Guatemala and a Synopsis of Species in Section Pauciflorae

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    As presently interpreted Phoradendron section Paucifiorae consists of 15 species. These mistletoes parasitize primarily conifers. We describe seven new species, make status changes for four species, and provide information on the hosts and distribution of all members of the section. New species described are: Phoradendron abietinurn Wiens, on Abies durangensi s in Chihuahua, Durango, and Jalisco, Mexico; P. acuminatum Wiens, on Cupressus lusitanica in Guatemala; P. flavomarginatum Wiens, on Juniperus fiaccida in Nuevo León, Mexico; P. lta wksworthii Wiens, on Juniperus in New Mexico, west Texas, and Coahuila, Mexico; P. olivae Wiens, on Cupressus lusitanica in Colima and Jalisco, Mexico; P. rufescens Wiens, on Juniperus spp . in San Luis Potosí, Mexico; and P. sedifolium Wiens on Cupressus lusitanica in Chiapas, and Hidalgo, Mexico. Three taxa previously recognized as subspecies are raised to specific rank: P. densum Torr. ex Trel., P. paucifiorum Torr., and P. libocedri (Engelm.) Howell. Also P. saltillense Trel., which had been placed in synonymy under P. botleanum subsp. densum, is accorded species status. In addition, three new epiparastic species of Phoradendron are described. Epiparastic mistletoes are known to parasitize only other species of mistletoes—in this instance Phoradendron or Cladocolea (Loranthaceae)

    Developmental Failure and Loss of Reproductive Capacity as a Factor in Extinction: A Nine-Year Study of Dedeckera Eurekensis (Polygonaceae)

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    Many long-lived perennial species exhibit lowered reproductive capacity. Early studies of reproductive success in Dedeckera eurekensis (Polygonaceae) demonstrated that the species exhibited extremely low reproductive success, low seed/ovule (S/O) ratios (i.e., the percentage of ovules that produce filled seeds; 2.5 %), low germinability of filled seeds (3.5%), low seedling survivorship (11 .1%), and lack of recruitment in natural populations. These results were attributed to genetic load, but this elicited controversy, prompting long-term studies of the relationship between the S/O ratio and environment. After nine years of monitoring, however, the S/O ratio had not changed significantly (2 .7%), and there was no significant correlation between precipitation and the S/O ratio. Controlled field experiments demonstrated that neither resource availability nor other ecological factors significantly influenced embryo abortion rates. Controlled self-pollinations (N = 115) matured only one questionably filled seed, whereas intrapopulation cross-pollinations (N = 192) produced significantly more seed (S/O = 12.0 %). Previous pollination studies demonstrated that the species has no primary pollinators and is only rarely visited by a few generalist insects. However, the flowers typically self-pollinate in 2—3 days following anthesis. Strong inference suggests that the loss of reproductive capacity in D. eurekensis may be the result of inbreeding depression due to the superimposition of self-pollination on a normally outcrossed species carrying a high genetic/segregational load


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    Volume: 21Start Page: 395End Page: 40