Tusam sumatra, dengan nama ilmiah Pinus merkusii, merupakan tumbuhan runjung (Pinophyta) dengan daun berbentuk jarum. Tumbuhan ini berumah satu, berarti organ kelamin jantan dan betina terpisah namun dalam satu individu. Bentuknya pohon dengan tajuk cenderung berbentuk kerucut, walaupun terdapat variasi yang cukup besar.

Tusam di Dataran Tinggi Gayo, mencapai ketinggian 70 m lebih.

Tumbuhan ini mendominasi hutan tropika pegunungan di Indonesia bagian barat pada ketinggian mulai dari 600 meter di atas permukaan laut hingga sekitar 1.500 meter, khususnya di Sumatra. Perum Perhutani membudidayakan tusam di sejumlah tempat di Jawa dan Sumatra untuk disadap getah batangnya, sebagai bahan baku terpentin dan gondorukem.

Pinus merkusii is a medium-sized to large tree, reaching 25–45 metres (82–148 feet) tall and with a trunk diameter of up to 1 m (3 ft 3 in). The bark is orange-red, thick and deeply fissured at the base of the trunk, and thin and flaky in the upper crown. The leaves ('needles') are in pairs, very slender, 15–20 centimetres (6–8 inches) long and less than 1 millimetre (1⁄32 in) thick, green to yellowish green.

The cones are narrow conic, 5–8 cm (2–3+1⁄4 in) long and 2 cm (3⁄4 in) broad at the base when closed, green at first, ripening glossy red-brown. They open to 4–5 cm broad at maturity to release the seeds. The seeds are 5–6 mm (3⁄16–1⁄4 in) long, with a 15–20 mm (1⁄2–3⁄4 in) wing, and are wind-dispersed.

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Pinus merkusii is closely related to the Tenasserim pine (P. latteri), which occurs farther north in southeast Asia from Myanmar to Vietnam; some botanists treat the two as conspecific (under the name P. merkusii, which was described first), but P. latteri differs in longer (18–27 cm or 7–10+1⁄2 in) and stouter (over 1 mm thick) leaves and larger cones with thicker scales, the cones often remaining closed for some time after maturity. It is also related to the group of Mediterranean pines including Aleppo pine and Turkish pine, which share many features with it.