nuta||Cytisus scoparius||Collinsia spp.|
|Crataegus douglasii||Gaultheria shallon||Crocidium multicaule|
|Fraxinus latifolia||Hedera helix||Cynosurus echinatus|
|Heteromeles arbutifolia||Holodiscus discolor||Dactylis glomerata|
|Juniperus scopulorum||Osmaronia cerasiformis||Danthonia californica|
|Libocedrus decurrens||Philadelphus lewisii||Delphinium menziesii|
|Lithocarpus densiflorus||Physocarpus capitatus||Dentaria californica|
|Pinus contorta||Purshia tridentata||Dodecatheon hendersonii|
|Pinus monticola||Rhus diversiloba||Dryopteris arguta|
|Pinus ponderosa||Ribes sanguineum||Elymus glaucus|
|Pinus sabiniana||Rosa eglanteria||Eriogonum nudum|
|Populus tremuloides||Rosa gymnocarpa||Eriophyllum lanatum|
|Populus trichocarpa||Rosa nutkana||Erythronium oregonum|
|Prunus avium||Rubus laciniatus||Festuca spp.|
|Prunus emarginata||Rubus parviflorus||Fritillaria lanceolata|
|Prunus virginiana||Rubus procerus||Galium spp.|
|Pseudotsuga menziesii||Rubus ursinus||Holcus lanatus|
|Pyrus communis||Spiraea betulifolia||Hypericum perforatum|
|Pyrus fusca||Spiraea douglasii||Lathyrus spp.|
|Pyrus malus||Symphoricarpos albus||Lomatium utriculatum|
|Quercus agrifolia||Symphoricarpos mollis||Lonicera ciliosa|
|Quercus chrysolepis||Symphoricarpos rivularis||Lotus micranthus|
|Quercus douglasii||Vaccinium ovatum||Lupinus spp.|
|Quercus kelloggii||Vaccinium parvifolium||Melica geyeri|
|Rhamnus purshiana||Viburnum ellipticum||Mimulus spp.|
|Salix spp.||Montia spp.|
|Sambucus cerulea||Nemophila heterophylla|
|Taxus brevifolia||Osmorhiza spp.|
|Thuja plicata||Phacelia linearis|
|Tsuga heterophylla||Platyspermum scapigera|
|Umbellularia californica||Plectritis spp.|
¹ Sources: 4,10,11,13,20,22,24,28,31,32,35,42,47,54,62,63,67,69,70,71,72,73,75,78
Flowering and Fruiting- Oregon white oak flowers somewhat later in the spring than many of its associates. Flowering has been noted in March, April, May, and June (72,74), but the seasonal span is probably greater over the wide range of latitudes and elevations where this species occurs. Flowers appear concurrently with new leaves and extension of twig growth.
The species is monoecious, bearing slim, staminate flowers (catkins) that emerge from buds on existing twigs and also appear on the basal end of developing twigs (64). Some catkins associated with new twig growth just originate from the same bud; others are located as much as 5 mm (0.2 in) from the base on new growth. Catkins are pale yellow tinged with green. Fully extended catkins vary greatly in length-in one collection, from 3 to 10 cm (1.2 to 3.9 in). Catkins of the same twig and cluster are in various stages of development-some are fading before others reach full size. The faded dry catkin is light brown and fragile.
The closed pistillate flowers are small, deep red, and covered with whitish hairs (64). They appear in axils of developing leaves, either single and sessile or as many as five or six on a short stalk up to 2 cm (0.8 in) long. Two flowers are often located at the base of the stalk and several along and at its tip. Basal flowers may be open while others on the stalk are still tiny and tightly closed. Flower openings are narrow; the interior elements are greenish to yellowish. Flowers were found on new growth that had extended only 1 cm (0.4 in) or up to 12 cm (4.7 in); most flowers were on new growth 4 to 7 cm (1.6 to 2.8 in) long. Flowering appears at its fullest when the first leaves are about half size; when leaves approach full size, catkins are withered. On a single tree, flowering seems to be a short event, perhaps a week long, as leaves develop quickly once growth starts.
Individual trees are known to flower abundantly, but observations are needed on the regularity of flowering and on the variability within and between stands and locations.
Seed Production and Dissemination- Seed crops may be heavy but are considered irregular. The large acorns, typically about 3 em (1.2 in) long and half as wide, mature in one season and ripen from late August to November. The age when a tree first bears fruit, the age of maximum prod