Description from Flora of China
Lycopodium centrochinense Ching; L. clavatum Linnaeus var. nipponicum Nakai; L. clavatum var. wallichianum Spring; L. interjectum Ching & H. S. Kung; L. kinabaluense Ching; L. pseudoclavatum Ching; L. pseudoclavatum var. yunnanense Ching; L. simulans Ching & H. S. Kung; L. taliense Ching; Stachygynandrum japonicum (Thunberg) P. Beauvois.
Stolons borne on ground, slender and creeping, 2 or 3 times forked, green, with sparse leaves; lateral branches erect, up to 40 cm tall, multiple times dichotomous, sparse, flattened (young branches terete), stem together with leaves 5-10 mm in diam. Leaves spirally arranged, dense, angled upward, lanceolate or linear-lanceolate, 4-8 × 0.3-0.6 mm, herbaceous, with transparent hairs, midrib indistinct, base cuneate, decurrent, sessile, margin entire, apex acuminate. Strobili (3 or)4-8 together on a peduncle, bracts of peduncle spirally arranged, sparse, thinly herbaceous, leaflike; strobili bearing different lengths of pedicels, erect, terete, 2-8 cm × 5-6 mm, pedicels 1-5 cm; sporophyll broadly ovate, 2.5-3.5 × ca. 2 mm, thinly leathery or papery, erose, with only narrow transparent membranous erose margin, apex acute, with long aristate tip. Sporangia slightly exposed.
The angles between branches and stems of Lycopodium japonicum are an unreliable character. The leaf shapes can vary too from one population to another depending upon the habitat. Thus, L. centrochinense, L. interjectum, L. kinabaluense, L. pseudoclavatum var. yunnanense, L. simulans, and L. taliense should be merged into L. japonicum.
Lycopodium japonicum, occurring in E and S Asia, is often misidentified as the European L. clavatum Linnaeus (e.g., Nakaike, New Fl. Japan, 17. 1982; J. L. Tsai & W. C. Shieh, Fl. Taiwan, ed. 2, 1: 31. 1994).
Lycopodium japonicum has entire leaves, and each of its fertile branches has 3-8 strobili with pedicels of different lengths.
Forests, shrubs, grassy slopes, roadsides, on rocks; 100-3300 m. Throughout China except N and NE China [Bhutan, Cambodia, India, Japan, Laos, Myanmar, Nepal, Vietnam; other countries of S Asia].