Lobelia yuccoides is a shrub characterized by its woody, erect stems that reach heights of 1.5–2 meters and feature a dense apical rosette of leaves. The leaves are simple and alternate with linear blades that measure 24–35 cm in length and 0.5–1.5 cm in width. The apex of each leaf is acute to acuminate. The upper surfaces of the leaves are glabrous, while the lower surfaces are white tomentose. The margins are entire or minutely callose-denticulate and revolute. The leaves are sessile or subsessile and lack stipules. The flowers emerge in unbranched inflorescences that span 60-100 cm long. Each flower is supported by an 8-12 mm long pedicel and pubescent. The bracts are subulate, measuring 20-30 mm long. The hypanthium is obconical and 4–6 mm long, with a pubescent surface. Each flower is bisexual (perfect) and features a calyx with five subulate lobes 3–6 mm long, with connate sepals and a tube adnate to the ovary. The corolla is zygomorphic (bilaterally symmetric), dorsally cleft almost to its base, and varies in color from blue to lilac. It measures 36-40 mm long and 3-5 mm wide and is pubescent. The lobes of the corolla are spirally revolute, and the tube is suberect. It has five stamens that alternate with the corolla lobes. The anthers are pubescent at the base, and the lower two feature apical tufts of white hair. The anthers are dithecal and open by longitudinal slits. They are coherent but can separate after anthesis or remain connate, forming a tube into which pollen is shed. The filaments may be distinct or connate above, attached to the epigynous nectary disk, or rarely adnate to the corolla tube. The ovary is inferior, 2-celled, often topped with an annular nectary disk, with axile placentation, or when 1-celled, it has two parietal placentas. The stigmas are 2-lobed, initially appressed and nonreceptive, as the style grows through the anther tube to push out the pollen, after which they spread apart and become receptive. The fruit is a loculicidal capsule that is obovoid to cylindrical, 10–12 mm long, and pubescent, opening at the apex by two valves. The seeds are numerous, smooth, brownish, and about 0.6-0.7 mm long, containing a straight, short to spatulate dicotyledonous embryo embedded in oily endosperm. It grows on dry ridges and canyons in diverse mesic forests between 750-1,200 meters.