Bulbs often somewhat purplish, variable, subrhizomatous to ± ovoid, 3.3-11.7 × 2.4-14.4 cm, 0.4-2.6(-3) times taller than long; scales unsegmented or notched, longest 3.5-11.2 cm; stem roots present or absent. Stems to 3.1 m. Buds rounded in cross section. Leaves in 2-8 whorls or partial whorls, 3-16(-28) leaves per whorl, usually ascending, 4.6-14.5 × 0.8-3.6 cm, 2.9-7.2 times longer than wide; blade usually ± oblanceolate, though often weakly so, rarely elliptic or lanceolate, margins usually undulate, apex acute; veins and margins ± smooth abaxially. Inflorescences racemose, 1-33(-40)-flowered. Flowers pendent, not fragrant; perianth Turk´s-cap-shaped; sepals and petals reflexed 1/5 along length from base, orange or yellow, with prominent red or magenta spots, not distinctly clawed; sepals not ridged abaxially, 5.2-9.8 × 1.4-2.4 cm; petals 5.6-9.6 × 1.5-2.9 cm; stamens strongly exserted; filaments parallel along most of length, then very widely spreading, diverging 17°-31° from axis; anthers purple, 1.1-1.9 cm; pollen rust, tan, or peach, becoming yellow or tan-yellow; pistil 4.6-7.1 cm; ovary 1.2-2.6 cm; style green, often pale; pedicel 7.8-21.2 cm. Capsules longitudinally keeled, 2.5-5.4 × 1.8-3.3 cm, 1.1-2.3 times longer than wide. Seeds not counted.

Lilium humboldtii is declining throughout its range due to habitat destruction, primarily for housing. Forming large scattered colonies at foothill elevations under ponderosa pines or in oak canyons and chaparral, these massive plants with towering inflorescences and large flowers are quite striking. With Lilium pardalinum and L. parryi, they were used in the early part of the century to produce the Bellingham hybrid lilies, development of which continued with the Bellmaid hybrids. Though not as popular as various Asiatic hybrids, these are still in use.

A. M. Kellogg was aware as early as 1859 that the tall, orange-flowered, dry-land lily from the foothills of the Sierra Nevada was distinctive, and he presented this opinion to the California Academy of Sciences about that time (A. M. Kellogg 1872). By the time he had published a description attached to the name Lilium bloomerianum, P. E. S. Duchartre had described this same plant from material provided by B. Roezl and grown by M. Leichtlin, and named it after the German explorer and botanist Alexander von Humboldt. Carl Purdy and others then misapplied Kellogg´s name in various combinations to the southern California expression recognized here as Lilium humboldtii subsp. ocellatum.

The Humboldt lily is pollinated primarily by large butterflies, especially western tiger swallowtails (Papilio rutulus Lucas, family Papilionidae) and pale swallowtails (P. eurymedon Lucas), and to a lesser extent by the monarch butterfly [Danaus plexippus (Linnaeus), family Nymphalidae].