Two Epiparasitic Species of Phoradendron (Viscaceae) from Honduras: one New and for the Other a Range Extension and Host Determination

A new species of Phoradendron, Ph. mathiasenii, is described, and a range extension and host are given for Ph. tikalense. Both species are from Honduras and grow as epiparasites, i.e., mistletoes parasitizing other mistletoes. The parasitic host for both epiparasitic species of Phoradendron is Psittacanthus angustifolius (Loranthaceae), which in turn is parasitic on the terrestrial host, Pinus oocarpa, a common forest tree in the collection area. Although the two species of Phoradendron parasitize the same parasitic host and co-occur in the area, they are distinct morphologically. Many plants of Ph. mathiasenii were observed at several collection sites in the study area while plants of Ph. tikalense were observed at only one site

Epiparasitism in Phoradendron durangense and P. falcatum (Viscaceae)

Phoradendron, the largest mistletoe genus in the New World, extends from temperate North America to temperate South America. Most species are parasitic on terrestrial hosts, but a few occur only, or primarily, on other species of Phoradendron. We examined relationships among two obligate epiparasites, P. durangense and P. falcatum, and their parasitic hosts. Fruit and seed of both epiparasites were small compared to those of their parasitic hosts. Seed of epiparasites was established on parasitic-host stems, leaves, and inflorescences. Shoots developed from the plumular region or from buds on the holdfast or subjacent tissue. The developing endophytic system initially consisted of multiple separate strands that widened, merged, and often entirely displaced its parasitic host from the cambial cylinder. During establishment the epiparasite invaded the cortex, vascular cylinder, and pith of its parasitic host and spread aggressively within host tissues, extending between and into individual host parenchyma cells, eventually isolating host cells or cell groups. The parasitic host showed little visual response to the epiparasite. Endophytic system growth of the epiparasite within its parasitic host was compared to that of a parasitic Phoradendron within its terrestrial host. The results indicate growth dynamics similar to those of parasitic species on terrestrial hosts. We conclude that the epiparasite/parasitic-host union should not be regarded as a graft union. The harmonious appearance of the union is a result of the growth of the epiparasite replacing entirely tissues of its parasitic host, with little or no hypertrophy of parasitic-host branches

Sinker Structure of Phoradendron californicum (Viscaceae) Confounds its Presumed Close Relationship to Other Acataphyllous Species

Phoradendron is the largest genus of New World mistletoes, with about 250 species in two subgenera, Boreales and Aequatoriales, corresponding, respectively, to northern acataphyllous and southern cataphyllous groups. The typically acataphyllous P. californicum of western North America is controversial because recent phylogenetic work has nested it in the southern cataphyllous clade. Seedling establishment, stem anatomy, and endophytic system structure of this species were studied. Seedling haustorial holdfasts have gland cavities, structures considered absent in the Viscaceae clade of Santalales. The stem epidermis has a thick cuticle, deeply sunken stomata, and branched multicellular trichomes. The stem has an outer cortex of palisade chlorenchyma and an inner cortex of large isodiametric parenchyma cells. The boundary area between the outer and inner cortex contains druses and an unusual ring of small xylic bundles lacking protoxylem fibers and phloem. Sinkers are of two types: uniseriate, with only parenchyma that often has thick-walled transfer cells at its interface with vessels of the host; and multiseriate, with parenchyma and vessel elements that often are in direct contact and share simple perforation plates with vessels of the host. Sinker morphology is also dimorphic in the cataphyllous P. fragile but only unimorphic (multiseriate) in the acataphyllous P. juniperinum and P. serotinum. The dimorphic sinker system of P. californicum may be functionally partitioned, whereas these functions are combined in the unimorphic sinkers of other acataphyllous species. Differences in sinker morphology may reflect evolutionary trends in Phoradendron. This study also supports the hypothesis that P. californicum is more closely aligned with the mainly tropical cataphyllous species of the genus

Formulation of a Mathematical Model for the Allocation of Colorado river Waters in Utah

A Mathematical model for the allocation of Utah’s water resources is formulated in the linear programming format. The availability of water from various sources is considered with the demands for water in each of the nine hydrologic study areas of Utah. The applications of mathematical models of this type are studied and the merits of the linear programming approach are discussed

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x, 545 hlm.: ill.; 24 cm

MORPHOLOGICAL ASPECTS OF SEEDLING ESTABLISHMENT IN FOUR TEMPERATE REGION PHORADENDRON (VISCACEAE) SPECIES

Volume: 48Start Page: 79End Page: 8