Caprifoliaceae (honeysuckle family): major woody family with opposite arrangement and it's not Aceraceae is how I remember this one. Native genera include Sambucus, Viburnum, Symphoricarpos, Lonicera and Linnaea. Two Lonicera examples are pictured here, the developing fruit of Lonicera involucrata (black twinberry) above and Lonicera ciliosa (orange honeysuckle) below.
Other w. WA native woody shrubs/trees genera/species with opposite arrangement besides the maples and the Caprifoliaceae members (there aren't that many): some Cassiope (moss-heather) species - Ericaceae, Ceanothus (snowbrush/ceanothus) - Rhamnaceae, Cornus (dogwood) - Cornaceae, Euonymous occidentalis (western burning bush) - Celastraceae, Fraxinus latifolia (Oregon ash) - Oleaceae, Paxistima myrsinites (Oregon boxleaf) - Celastraceae, Philadelphus lewisii (mock-orange) - Hydrangeaceae and Whipplea modesta (common whipplea/modesty) - Hydrangeaceae.
Besides the two pictured here there are four other w. WA native Lonicera species: L. caerulea (bluefly honeysuckle), L. utahensis (rocky mountain h.), L. conjugialis (purple-flower h.), and L. hispidula (hairy h.). L. caerulea exhibits yellow blooms, L. utahensis light yellow to creamy white blooms, L. conjugialis has purple blooms (hence the common name) and L. hispidula has pink flowers.
Patters of the Honeysuckle family according to Elpel: shrubs with opposite leaves, pithy stems, and the flowers and fruits often form in pairs; those that are in bunches are sometimes in pairs within the bunches. And here are some terms and generalities, according to Hitchcock: indehiscent, generally fleshy fruit with copious endosperm. Estipulate leaves. Flowers in various sorts of inflorescences of generally cymose origin.
Gamopetalous = with the petals united, at least partially. Cymose = with flowers in a cyme. Cyme = a flat-topped or round-topped determinate inflorescence, paniculate, in which the terminal flower blooms first.
