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Tree 15–35 m, 0.6 m dbh. Bark smooth, brown, quickly becoming fissured; in older trees, scaly. Crown conical when young, columnar in old trees. Branchlets slender, glabrous, shiny light reddish brown, becoming grey in the grooves in the second year and subsequently all over; lightly covered with whitish resin in the first winter, the linear ridges on the first-year shoots ending in the very short free and largely appressed pulvinus; short shoots cylindrical, broader than long, 0.2–0.45 × 0.45–0.6 cm; vegetative buds resinous, rounded conical, 0.3–0.4 cm. Leaves bright green, turning yellow in autumn, 0.9–2.2 × 0.06–0.11 cm, linear-oblong, straight or slightly falcate, only keeled adaxially and at the base abaxially, apex obtuse; c.30–50 leaves per short shoot. Male strobili broadly conical, shortly pedunculate, 0.6–0.8 × 0.55–0.65 cm long, reddish. Female cones on 1–1.3 cm peduncles, oblong-ellipsoid, 3–5 2.2–2.5 cm, purple-brown to grey-brown; seed scales c.60–75, broadly obovate-reniform, 0.8–1 × 1 cm, minutely white-hairy on the broadly rounded, entire or shallowly retuse apices; bracts exserted, c.1.8 cm, reflexed to strongly reflexed, lanceolate, dark purple-brown, 0.5 cm broad where they emerge, gradually tapering, then abruptly into a 0.15–0.4 cm cusp; seed 0.3 × 0.2 cm, with wing 0.6–0.7 × 3 mm. Mill 1999. Distribution CHINA: southeast Xizang. Habitat Mountain slopes between 3200 and 3500 m asl. USDA Hardiness Zone 7. Conservation status Not evaluated. Illustration NT439. Taxonomic note This species was described in 1999 but was placed by Farjon (2001) in synonymy with L. griffithii, though it differs in several important features, notably its smaller cones (3–5 cm, vs. 5–8(–11) cm) and other reproductive parts. Larix kongboensis has glabrous, darker-coloured shiny shoots (vs. yellowish brown and matt in L. griffithii), flecked with resin on vigorous shoots; it has resinous buds (vs. non-resinous), short shoots that are wider than they are long, and shorter, narrower leaves (0.9–2.2 cm × 0.6–1.1 mm, vs. 2.5–5.5 cm × 1.0–1.8 mm). It differs from L. himalaica in its reflexed bracts (vs. nearly straight), which are 8 mm longer than the seed scales (vs. only slightly exserted), in its smaller seed scales (8–10 mm, vs. 12–15 mm) and narrower cones (2.2–2.5 cm, vs. 2.8–3.2 cm), and in its reddish brown (vs. yellow or yellow-brown) shoots.
As well as being distinct in terms of morphological characters, as outlined above, Larix kongboensis occurs on the drier northern side of the Himalaya, occupying the valleys draining northwards into Tibet, whereas L. griffithii is from the much wetter southern slopes in eastern Nepal, Sikkim, Bhutan and Arunachal Pradesh. According to Keith Rushforth (pers. comm. 2007) it was first collected by Frank Kingdon-Ward in 1924, and then by Frank Ludlow and George Sherriff in the 1930s, but was misidentified as L. griffithii or L. mastersiana. If it was introduced by these earlier collectors there is no record of surviving plants. Gatherings were made by Keith Rushforth in 1995 from the Doshong La (KR 3431) and from Pasum Tso (KR 3795), and it is now found in a number of collections in the United Kingdom, where it is doing well. At Tregrehan it has made a tree 4 m in height with a dbh of 10 cm, and is coning freely (K. Rushforth, pers. comm. 2008).