Lobelia gloria-montis subsp. longibracteata is 2.4–5 m in height and 2–10 cm in diameter, with stems 2–4 m long. Leaves are simple and alternate, with oblanceolate blades measuring 18–23 cm long and 1.8–4.3 cm wide. The leaf apex is acute or acuminate, and the base is attenuate, cuneate, or obtuse. Surfaces are glabrous, though the margins may be ciliate near the base. Margins are subrevolute or merely thickened, and stipules are absent. The inflorescence is 1–1.5 m tall, unbranched or 5–7-branched, with each branch bearing 40–80 flowers. Floral bracts are oblong or linear, 60–90 mm long and 6–10 mm wide; pedicels are 38–60 mm long. Flowers are bisexual (perfect), with a broadly campanulate, pubescent hypanthium 10–13 mm long and 11–18 mm in diameter. The calyx has 5 narrowly triangular lobes, 25–35 mm long and 5–9 mm wide, 2–3.5 times longer than the hypanthium. The corolla is white, glabrous, zygomorphic (bilaterally symmetrical), and dorsally cleft almost to the base, 78–103 mm long, with a slightly curved tube 28–44 mm long and 12–15 mm wide. Dorsal lobes are 45–70 mm long, and the ventral lip is 40–52 mm long and 22–26 mm wide. Stamens are 5, with anthers bearing apical tufts of white hairs; the filament tube is 68–82 mm long, the anther tube 4.5–6 mm in diameter, dorsal anthers 15–17 mm long, and ventral anthers 11–13 mm long. The ovary is inferior and 2-celled, often with an annular nectary disk; stigmas are 2-lobed and become receptive after pollen is pushed through the anther tube. Fruits are loculicidal capsules, 33–36 mm long and 14–18 mm in diameter, dehiscing at the apex by 2 valves. Seeds are numerous, chestnut-brown, with a straight, short to spatulate embryo embedded in oily endosperm. It occurs in montane wet forests, between 1,280–1,750 meters.