- Group 1Lycophytes, Monilophytes
- Group 2Gymnosperms
- Group 3Monocots
- Group 4Woody angiosperms with opposite or whorled leaves
- Group 5Woody angiosperms with alternate leaves
- Group 6Herbaceous angiosperms with inferior ovaries
- Group 7Herbaceous angiosperms with superior ovaries and zygomorphic flowers
- Group 8Herbaceous angiosperms with superior ovaries, actinomorphic flowers, and 2 or more distinct carpels
- Group 9Herbaceous angiosperms with superior ovaries, actinomorphic flowers, connate petals, and a solitary carpel or 2 or more connate carpels
- Group 10Herbaceous angiosperms with superior ovaries, actinomorphic flowers, distinct petals or the petals lacking, and 2 or more connate carpels
Spinulum is the sister genus to Lycopodium, and the two genera share such features as terete branches, superficial horizontal shoots, and non-dendroid upright shoots. However, they differ in many important features such as phyllotaxis, leaf apex morphology, and branching pattern of upright shoots. The trophophylls change actual length and relative length to width through the growing season. Therefore, to enable consistent comparisons, measurements and counts performed on trophophylls should be assessed on those near the middle of seasonal growth unless specified otherwise.
1a. Trophophylls of upright shoots with abundant stomates on the adaxial surface (i.e., 25–53 per ½ surface), 3–5.9 mm long, entire or very obscurely toothed, arranged in alternating pseudowhorls of 4, those immediately above the winter bud constrictions triangular to lanceolate or narrow-ovate (i.e., broadest at or very near the base); strobili 8–17 (–21) mm tall
1b. Trophophylls of upright shoots lacking stomates on upper surface (except the trophophylls at and immediately above winter bud constrictions), 5.2–9.8 mm long, obscurely to evidently toothed, arranged in alternating pseudowhorls of 5, those immediately above the winter bud constrictions oblanceolate or sometimes elliptic (i.e., broadest at or above the middle); strobili (15–) 17–43 mm tall
Show photos of: Each photo represents one species in this genus.