Lycopodiopsida
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 Lycopodiella cernua with close-up of branch
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The class Lycopodiopsida includes the clubmosses. These plants are often loosely grouped as the fern allies. The Lycopodiopsida traditionally included all the clubmosses, including Selaginella and Isoetes. However, subdivisions within the Division Lycopodiophyta are now considered ancient enough to warrant higher-level separation in accordance with cladistics.
The clubmosses are thought to be structurally similar to the earliest vascular plants, with small, scale-like leaves, homosporous spores borne in sporangia at the bases of the leaves, branching stems (usually dichotomous), and generally simple form.
The Class Lycopodiopsida as interpreted here contains a single living order, the Lycopodiales, and a single extinct order, the Drepanophycales.
[edit] Order Lycopodiales
The classification of this group has been unsettled in recent years and a consensus is yet to emerge. Older classifications took a very broad definition of the genus Lycopodium that included virtually all the species of Lycopodiales. The trend in recent years has been to define Lycopodium more narrowly and to classify the other species into several genera, an arrangement that has been supported by both morphological and molecular data and adopted in numerous revisions and flora treatments. These genera fall into two distinct groups but there is as yet no consensus as to whether to recognize them in a single family, Lycopodiaceae, or to separate them into two families: a more narrowly defined Lycopodiaceae and Huperziaceae.
Lycopodiaceae, as narrowly defined, comprises the extant genus, Lycopodium, which includes the Wolf's-foot clubmoss, Lycopodium clavatum, Ground-pine, Lycopodium obscurum, Southern ground-cedar, Lycopodium digitatum, and other species. Also included are species of Lycopodiella, such as the Bog clubmoss, Lycopodiella inundata. Most of the Lycopodium favor acidic, sandy, upland sites, whereas most of the Lycopodiella favor acidic, boggy sites.
The other major group, the Family Huperziaceae, are known as the firmosses. This group includes the genus Huperzia, such as the Shining firmoss, Huperzia lucidula, the Rock firmoss, Huperzia porophila, and the Northern firmoss, Huperzia selago. This group also includes the odd, tuberous Australasian plant Phylloglossum, which was, until recently, thought to be only remotely related to the clubmosses. However, recent genetic testing has shown it to be very closely related to the genus Huperzia.
A powder known simply as lycopodium, consisting of dried spores of the common clubmoss, was used in Victorian theater to produce flame-effects. A blown cloud of spores burned rapidly and brightly, but with little heat. It was considered safe by the standards of the time.
