The lycophytes are sister to the other vascular plants

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The club mosses and their relatives, the spike mosses and quillworts, are collectively called lycophytes. The lycophytes are the sister clade to the remaining vascular plants (see Figure 27.1B). There are relatively few (just over 1,200) surviving species of lycophytes.

The lycophytes have true roots that branch dichotomously. The arrangement of vascular tissue in their stems is simpler than in other vascular plants. They bear simple leaflike structures called microphylls, which are arranged spirally on the stem (Figure 27.14A). Growth in lycophytes comes entirely from apical cell division. Branching in the stems, which is also dichotomous, occurs by division of an apical cluster of dividing cells.

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Figure 27.14 Lycophytes and Monilophytes (A) Club mosses have microphylls arranged spirally on their stems. Strobili are visible at the tips of these stems. (B) Horsetails have a distinctive growth pattern in which the stem grows in segments above each whorl of leaves. These are fertile shoots with sporangia-bearing structures at the apex. (C) The floating leaves of a water fern. (D) Tree ferns dominate this forest in Oparara Basin Kahurangi National Park in New Zealand.

The sporangia of many club mosses are aggregated in conelike structures called strobili (singular strobilus; see Figure 27.14A), which are clusters of spore-bearing microphylls attached to the end of the stem. Other club mosses lack strobili and bear their sporangia on (or adjacent to) the upper surfaces of specialized microphylls.