1D Leaves 4 ranked - Diphasiastrum*
2B Leaves all same length
3B Branches square in cross section; trowel shaped leaves; < 12 cm - Di. alpinum
3A Branches flattened; leaves at base of strobili widely spaced - Di. sabinifolium
2A Top and bottom leaves shorter than lateral leaves
4C 4(3) strobili; glaucous blue color; branches square in cross section - Di. tristachyum
4B 2-4 strobili; very regularly fan-shaped branches - Di. digitatum
4A 1-2 strobili; annular constrictions visible; irregular leaf pattern - Di. complanatum
1C Leaves 5 ranked - Diphasiastrum sitchense
1B Leaves 6 ranked - Dendrolycopodium
5B Lateral leaves form single horizontal plane; branches flattened - De. dendroideum
5A Top and bottom leaves form single verticle plane
6B Bottom leaf rank much shorter than others - De. obscurum
6A All leaf ranks same length - De. hickeyi
1A Leaves more than 6 ranked or ranks indistinguishable (unranked)
7D Lacking strobili; sporangia in zones on upright stems; leafy gemmae branchlets present - Huperzia*
8B Leaves distinctly toothed obovate; woodland - H. lucidula
8A Leaves entire or weakly toothed
9B Apical leaves nearly the same size as basal; gemmae in single whorl at branch tips; boreal, cool, damp habitats; .... H. selago
9A Apical leaves smaller than basal
10C Gemmae in 1-3 whorls at branch tips; apical leaves 5-8 mm, basal 3-6 mm, leaves mostly narrowly lanceolate, parallel sided; sandstone substrate .... H. porophylla
10B Gemmae scattered along upright branches; apical leaves (2.5-3 mm) 1/2 of basal (4-6 mm); alpine & subalpine .... H. appressa
10A Gemmae in 2-3 whorls at branch tips; apical leaves (3.5-5.5 mm) 2/3 of basal (4.5-7 mm); .... H. miyoshiana
7C Strobili stalked; leaf tips with long hair tip - Lycopodium
11B Branches often with 2 or more strobili - Lm. clavatum
11A Branches with single strobili (rarely 2, if so attached at same point) - Lm. lagopus
7B Strobili leafy; upright shoots never branched; plants of bogs and wet places - Lycopodiella*, Pseudolycopodiella
12B Plants typically <10 cm - La. inundata
12A Plants typically >10 cm
13C Upright stems with sparse widely spaced leaves; horizontal stems often subterranean - P. caroliniana
13B Strobili barely wider than stem - La. appressa
13A Stobili much wider than stem; horizontal stems arched - La. alopecuroides
7A Strobili sessile; upright stems 1-2X branched - Spinulum
14B Strobili >1.5cm (to 4.5cm); leaves broadest at middle - S. annotinum
14A Strobili <1.5cm; leaves broadest at base - S. canadense
Dendrolycopodium - Ground Pine (3)
Diphasiastrum - Ground Cedar (5)
Huperzia - Firmoss (5)
Lycopodiella - Bog Clubmoss (3)
Lycopodium - Staghorn Clubmoss (2)
Pseudolycopodiella - False Bog Clubmoss (1)
Spinulum - Bristly Clubmoss (2)
With the revision of this family in the 1990s and 2000s, several common names now refer to multiple species and even multiple genera. In addition, many of the species already had multiple or regional common names. The common names below seem to represent a logical flow that is used by many, but certainly not all, authorities.
Dendrolycopodium dendroideum - Common Groundpine
Dendrolycopodium hickeyi - Pennsylvania Groundpine
Dendrolycopodium obscurum - Flattened Groundpine
Diphasiastrum alpinum - Alpine Clubmoss
Diphasiastrum complanatum - Northern Ground Cedar
Diphasiastrum digitatum - Southern Ground Cedar
Diphasiastrum sitchense - Sitka Clubmoss
Diphasiastrum tristachyum - Blue Ground Cedar
Diphasiastrum sabinifolium - Savinleaf Ground Cedar
Huperzia appressa - Mountain Firmoss
Huperzia lucidula - Shining Firmoss
Huperzia miyoshiana - Pacific Firmoss
Huperzia porophila - Rock Firmoss
Huperzia selago - Northern Firmoss
Lycopodiella alopecuroides - Foxtail Bog Clubmoss
Lycopodiella appressa - Southern Bog Clubmoss
Lycopodiella inundata - Northern Bog Clubmoss
Lycopodium clavatum - Staghorn Clubmoss
Lycopodium lagopus - One-Cone Clubmoss
Pseudolycopodiella caroliniana - Slender Bog Clubmoss
Spinulum annotinum - Bristly Clubmoss
Spinulum canadense - Northern Bristly Clubmoss
Nearly all clubmosses seem to cross within genera. Clubmosses that have characteristics intermediate to those in the key could reasonably be considered hybrids. Several species are likely fertile hybrids. Other hybrids are likely to exist including back crosses of hybrids with a parent species, even when the parent species is absent from the region. True sterile hybrids can be recognized by abortive or polymorphic spores. Recognized hybrids are listed below.
In addition clubmosses seem to readily form ecotypes with significant variations between those growing in shade versus sun or at elevation.
Diphasiastrum xhabereri (digitatum X tristachyum)
Diphasiastrum xissleri (alpinum X tristachyum)
Diphasiastrum sabinifolium (sitchense X tristachyum)
Diphasiastrum xverecundum (complanatum X digitatum)
Diphasiastrum xzeilleri (complanatum X tristachyum)
Huperzia xbartleyi (lucidula X porophila)
Huperzia xbuttersii (lucidula X selago)
Huperzia xjosephbeitelii (appressa X selago)
Huperzia porophylla (lucidula X appressa)
Huperzia xprotoporophylla (lucidula X appressa)
Lycopodiella xbrucei (appressa X prostrata)
Lycopodiella xcopelandii (appressa X alopecuroides)
Lycopodiella margueritae (inundata X alopecuroides)
Lycopodiella xrobusta (inundata X alopecuroides)
Lycopodiella subappressa (inundata X appressa)
Lycopodiella xgilmanii (inundata X appressa)
Sincere thanks to Arthur Haines for his corrections and comments.
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last update 2022-Jan-26