Don't blame the Palo Verde for your bad allergies
I am not sure why, but plants with yellow flowers get a bad rap amongst those who suffer from allergies. It might be a timing thing: palo verdes (Parkinsonia spp.) bloom during the spring, when the wind is terrible, and many wind-pollinated plants are blooming, especially the grasses. But the source of your misery might be misdirected.
A little botany lesson: plants that rely on wind pollination DO have a certain look: flowers of such species tend to have less conspicuous color, often are catkin-like, with petals that aren't showy and impeding the wind from lifting the pollen from the stamens (male part of the flowers producing and presenting pollen)--often these flowers have no petals at all. Almost all grass species are wind-pollinated. Conifers are too. The higher in elevation and latitude you go, the more wind pollination is more prevalent. Also, species that tend to pioneer disturbed areas (often plants that are considered weeds) are also wind pollinated. It makes sense: open landscapes offer more of a chance of success for a species relying on the risky and somewhat random mode of pollen transfer of wind.
The closer you get to the tropics, the less wind-pollination you see and the more that animals and insects are relied upon. The flowers in these species become more conspicuous, and another important difference occurs: nectar.
Plants that don't rely on the wind offer rewards for mobile species and that reward is present in every flower. The insect or animal, in collecting this reward, inadvertently transfers pollen from one flower to another, if that organism happens to visit another flower of the same species or even same plant.
The story of pollination is complicated and interesting though beyond the scope of this article, and you should read more about it. But for the sake of this article, understand that the pollen and flowers of such plants have characteristics different from wind-pollinated plants.
Flowers of animal/insect-pollinated plants produce way less pollen. And that pollen has a sticky nature (so as to stick to the nectar-probing organism). This sort of pollen is also not as easily captured by the wind since the flower is usually more elaborate, and blocking the stamens from having all their pollen blown off.
Back to the palo verdes: the typical pollinators for these trees are beetles, flies (not the kind that hangs out around garbage cans, but the kind that like flowers), and bees (both the solitary and social species). Palo verdes have sticky pollen that attaches itself to the insects while they go from flower to flower collecting nectar. It isn't impossible that some of that pollen may take flight into the wind. But when the allergy season is upon us and those trees are blooming, you might start looking around for other species that may be the actual culprits of your misery: the grasses are the worst--they are everywhere. Especially Bermuda grass (Cynodon dactylon), and now the ever-encroaching buffelgrass (Pennisetum cilare). If you are on the outskirts of town, or in an area with more natural vegetation, the other terrible spring allergen is the various species of ragweed (Ambrosia spp.). Mulberry and olive trees are terrible allergens. But they've become rarer in the landscape, and unless you are actually near such trees, it is most likely a grass that is irritating your sinuses.