Platanus racemosa is a species of sycamore tree known by several common names, including California sycamore, Western sycamore, California plane tree, and in Spanish Aliso. It is native to California and Baja California, where it grows in riparian areas, canyons, floodplains, at springs and seeps, and along streams and rivers in several types of habitats.
Trees , to 15(-25) m, rather massive; trunks sometimes straight and erect, more commonly irregular, reclining, or prostrate with branches irregular and sometimes near ground, to 2+m diam. Leaves: stipules entire to somewhat dentate. Leaf blade dark green, 3-5-lobed, 10-25 × 10-25 cm, rather thick; lobes of blade mostly longer than wide, basal lobes usually somewhat smaller and spreading, not reflexed, sinuses broad and deeply concave, depth of distal sinuses about 1/3-2/3 distance from sinus to base of blade, terminal leaf lobe ca. 1/3-2/3 length of blade; margins entire to remotely serrulate, apex acute to acuminate, sometimes rounded; surfaces abaxially persistently tomentose, adaxially glabrescent. Pistillate inflorescences: heads (1-)2-7; fruiting heads 20-25(-30) mm diam., lateral ones sessile; fruiting rachis to 25 cm. Achenes 7-10 mm, basal hairs about 2/3 length of achenes. 2 n = 42.