Huperzia

The sporophytes of this genus have unbranched shoots that are generally upright and round in cross section. Horizontal stems are absent. The leaves are not borne in distinct ranks, and are usually somewhat lanceolate in shape. In some species, they vary in size according to the season in which they grow. Branchlets bearing gemmae – bud-like structures by which the plant reproduces asexually – occur among the leaves. The gemmae are triangular, with eight leaves in a constant pattern: four flattened into a plane and two large lateral leaves. The sporangia are kidney-shaped (reniform), occurring at the base of a leaf that is either unmodified or reduced. The roots are produced near the apex of shoots, and migrate downwards inside the cortex of the stem to emerge at soil level. The unbranched gametophytes are not photosynthetic, but rather subterranean and mycorrhizal.[2]

The Flora of North America distinguishes Huperzia from the epiphytic tropical genus Phlegmariurus on the basis of differences such as the former's complex and specialized shoots, the gemmae and the branchlets on which they are borne, and the unbranched gametophytes.[2]

The genus Huperzia was created by Johann Jakob Bernhardi in 1801. Bernhardi separated Huperzia from Lycopodium. The type species is Lycopodium selago which became Huperzia selago.[1]

In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), Huperzia is placed in the subfamily Huperzioideae of the family Lycopodiaceae.[3] A phylogenetic study in 2016, employing both molecular and morphological data, concluded that either a one-genus or a three-genus division of the subfamily produced monophyletic taxa. The authors preferred the three-genus division, recognizing Huperzia, Phlegmariurus and Phylloglossum. Their preferred hypothesis for the relationships of the three genera was:[6]

The majority of the species formerly placed in a broadly defined Huperzia belong in Phlegmariurus.[6] Earlier, the Flora of North America had also separated Huperzia from Phegmariurus.[2] However, Phlegmariurus is difficult to separate morphologically, and others have preferred the one-genus division of the subfamily.[7][5]

As circumscribed in the PPG I classification, Huperzia is distributed in temperate, arctic and alpine habitats, including mountains in tropical Asia.[4] Its species are terrestrial or grow on rocks.[2] Phlegmariurus is epiphytic,[2] and has a worldwide tropical distribution,[7] so when Huperzia is defined broadly to include all three genera of the subfamily Huperzioideae, it has an almost worldwide distribution, absent mainly in North Africa, the Arabian Peninsula and Western Asia.[5]

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