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Plant of the Month: August 2009

hybrids of Seattle native tree species
    Hybrid plants are very commonly cultivated, but are infrequent in the wild. Hybrids can be between two species in a genus, or can even rarely be a cross of two genera ("inter-generic"). The economic import of hybrids to humans is enormous: wheat is the world's dominant calorie source, and is a hybrid. Intentional hybridizers can seek many goals when they breed plants. For example: disease resistance; cold-hardiness; heavier yields; new colors; more rapid growth; earlier ripening, and so on.
    Some beginner gardeners confuse cultivars and hybrids. A cultivar may or may not be of hybrid origin; it is merely a named cultivated variant. And most hybrids that have occurred either in the wild or in cultivation, never end up being cultivated extensively --if at all. People choose the best hybrids and tend to grow them often.
    With the global dispersal of both weedy and cultivated plant species, in some cases plant hybrids have more or less replaced certain species. For example, in England there are two native hawthorn species (Crataegus monogyna and C. laevigata), and their hybrid (C. × media). But the C. laevigata species is relatively rare now compared to the C. monogyna species, or to the hybrid.
    My intent had been to compile a checklist of all the hybrids involving plant species native in or near Seattle. But to begin with, I offer only the tree hybrids, inasmuch as in short order I came up with a list of 41 such crosses, and am certain that others exist. Seattle has 33 tree species which were, are, or may be native in the city:

    Red ALDER (Alnus rubra)
    Sitka ALDER (Alnus sinuata)
    Oregon ASH (Fraxinus latifolia)
    Paper BIRCH (Betula papyrifera)
    CASCARA (Rhamnus Purshiana)
    Western Red CEDAR (Thuja plicata)
    Bitter CHERRY (Prunus emarginata)
    Pacific CRABAPPLE (Malus fusca)
    Pacific DOGWOOD (Cornus Nuttallii)
    Douglas FIR (Pseudotsuga Menziesii)
    Grand FIR (Abies grandis)
    Black HAWTHORN (Cratægus Douglasii)
    Black HAWTHORN (Cratægus Suksdorfii)
    Western HEMLOCK (Tsuga heterophylla)
    MADRONA (Arbutus Menziesii)
    Bigleaf MAPLE (Acer macrophyllum)
    Dwarf MAPLE (Acer glabrum)
    Vine MAPLE (Acer circinatum)
    Oregon White OAK (Quercus Garryana)
    Lodgepole/Shore PINE (Pinus contorta)
    Western White PINE (Pinus monticola)
    Aspen (POPLAR) (Populus tremuloides)
    Black Cottonwood (POPLAR) (Populus balsamifera ssp. trichocarpa)
    Western SERVICEBERRY (Amelanchier alnifolia)
    Sitka SPRUCE (Picea sitchensis)
    Geyer WILLOW (Salix Geyeriana var. meleina)
    Mackenzie WILLOW (Salix eriocephala ssp. mackenzieana)
    Pacific Black WILLOW (Salix lucida ssp. lasiandra)
    Hooker Pussy-WILLOW (Salix Hookeriana)
    Piper Pussy-WILLOW (Salix Piperi)
    Scouler Pussy-WILLOW (Salix Scouleriana)
    Sitka Pussy-WILLOW (Salix sitchensis)
    Pacific YEW (Taxus brevifolia)

Below are 41 tree hybrids reported between the above-listed species native in Seattle, and non-native species. The crosses can have occurred either in the wild or by people, and can have occurred elsewhere than in Seattle. Most of the hybrids cannot be found in Seattle; perhaps a dozen exists here. The most common such cross on the list, in Seattle, is likely the ornamental dogwood called 'Eddie's White Wonder'. It is a sterile hybrid of much beauty, and resists the leaf anthracnose disease that disfigures both of its parental species.

Abies grandis × A. concolor
    This fir cross occurs in the wild.
Acer circinatum × A. japonicum
    This maple cross occured in cultivation in a Shoreline garden but its hybridity is unconfirmed.
Acer circinatum × A. palmatum 'Herbsfeuer'
    This maple cross occured in cultivation but its hybridity is unconfirmed.
Amelanchier alnifolia × Sorbus scopulina = ×Amelosorbus Jackii Rehd.
    This serviceberry / mountain ash cross occurs in the wild.
Betula papyrifera var. commutata × B. neoalaskana = B. ×Winteri Dugle
    This birch cross occurs in the wild. Other crosses occur of typical Betula papyrifera.
Betula papyrifera var. commutata × B. occidentalis = B. ×Piperi Britt.
    This birch cross occurs in the wild. Other crosses occur of typical Betula papyrifera.
Cornus Nuttallii × C. florida ('Ascona', 'Eddiei's White Wonder', 'Ormonde')
    These dogwood crosses occured in cultivation intentionally and accidentally.
Cornus Nuttallii × C. Kousa (Starlight®, Venus®)
    This dogwood cross occured in cultivation intentionally.
Cratiægus Suksdorfii × C. monogyna
    This hawthorn cross occurs in the wild.
Malus fusa × M. domestica (M. pumila) = M. ×Dawsoniana Rehd.
    This crabapple / apple cross occurs in the wild --even in Seattle, but was first noted in cultivated trees.
Picea sitchensis × P. glauca = P. ×Lutzii Little
    This spruce cross occurs in the wild.
Pinus contorta × P. Banksiana = P. ×Murraybanksiana Righter & Stockwell
    This pine cross occurs in the wild.
Pinus monticola × P. Ayacahuite
    This pine cross occured in cultivation intentionally.
Pinus monticola × P. flexilis
    This pine cross occurs in the wild.
Pinus monticola × P. Peuce
    This pine cross occured in cultivation intentionally.
Pinus monticola × P. Strobus
    This pine cross occured in cultivation.
Pinus monticola × P. Wallichiana
    This pine cross occured in cultivation intentionally.
Populus balsamifera ssp. trichocarpa × P. balsamifera = P. 'Balsam Spire'
    This cottonwood cross occurs in the wild.
Populus balsamifera ssp. trichocarpa × P. Fremontii = P. ×Parryi Sarg.
    This cottonwood cross occurs in the wild.
Populus balsamifera ssp. trichocarpa × P. nigra = P. 'Roxbury'
    This cottonwood / poplar cross occured in cultivation intentionally.
Populus balsamifera ssp. trichocarpa × P. nigra var. betulifolia = P. 'Andover'
    This cottonwood / poplar cross occured in cultivation intentionally.
Populus balsamifera ssp. trichocarpa × P. Maximowiczii = P. 'Androscoggin'
    This cottonwood / poplar cross occured in cultivation intentionally.
Populus tremuloides × P. alba = P. ×Heimburgeri Boivin
    This aspen / poplar cross occurs in the wild.
Populus tremuloides × P. angustifolia = P. ×Sennii Boivin
    This aspen / cottonwood cross occurs in the wild.
Populus tremuloides × P. balsamifera = P. ×Dutillyi Lepage
    This aspen / poplar cross occurs in the wild.
Populus tremuloides × P. deltoides = P. ×Bernardii Boivin
    This aspen / cottonwood cross occurs in the wild.
Populus tremuloides × P. grandidentata = P. ×Smithii Boivin, P. ×Barnesii W.H. Wagner
    This aspen cross occurs in the wild.
Populus tremuloides 'Pendula' × P. tremula 'Pendula' = P. 'Hiltingbury Weeping'
    This weeping aspen cross occured in cultivation intentionally.
Prunus emarginata × P. avium = P. ×pugetensis A.L. Jacobson & Zika
    This cherry cross occurs in the wild --even in Seattle.
Prunus emarginata × P. pensylvanica
    This cherry cross occurs in the wild in Canada.
Quercus Garryana × Q. Douglasii = Q. ×Eplingii C.H. Muller
    This oak cross occurs in the wild.
Quercus Garryana × Q. dumosa = Q. ×Howellii Tucker
    This oak cross occurs in the wild.
Quercus Garryana × Q. durata = Q. ×subconvexa Tucker
    This oak cross occurs in the wild.
Quercus Garryana × Q. lobata
    This oak cross occurs in the wild.
Salix Geyeriana × S. pedicellaris = S. ×Dieckiana Suksdorf
    This willow cross occurs in the wild.
Salix lucida ssp. lasiandra × S. Bonplandiana
    This willow cross occurs in the wild.
Salix sitchensis × S. alba
    This willow cross has been reported in Croatia, as a triploid.
Salix sitchensis × S. lasiolepis
    This willow cross occurs in the wild.
Thuja plicata × T. occidentalis
    This cedar cross occured in cultivation.
Thuja plicata × T. Standishii = T. 'Green Giant' ('Giganteoides')
    This cedar cross occured in cultivation intentionally.
Tsuga heterophylla × T. Mertensiana = T. ×Jeffreyi (Henry) Henry
    This hemlock cross occurs in the wild but was first noted in cultivated trees. Some taxonomists rank it as a variant of T. Mertensiana.

    By and by I intend to lengthen the above list, after doing more library work. If any readers care to help by e-mailing me addition data, I will be grateful.

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Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert
Arthur Lee Jacobson plant expert

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