Fig. 16.1-5a and b. Transverse sections of conifer needles. Most conifers have needle-shaped or scale-like leaves that remain alive for years, but their sieve cells last only a few months. These long-lived leaves have a vascular cambium that produces new secondary phloem every year. But the cambium does not produce any more xylem: it is a unifacial, unidirectional, persistent vascular cambium. The upper micrograph shows the secondary phloem in the needle leaf of pine (Pinus monophylla) and the lower one is a leaf of yew (Taxus). Long-lived leaves of dicots can also have secondary phloem along the midrib and larger veins. See pages 254, 255 and Fig. 12.35 in Plant Anatomy (Mauseth).
Only larch (Larix), bald cypress (Taxodium) and dawn redwood (Metasequoia) are deciduous, with leaves that persist for less than a year).