Cambial variations of Piper (Piperaceae) in Taiwan
Yang and Chen Bot Stud
Cambial variations of Piper (Piperaceae) in Taiwan
Sheng‑Zehn Yang 0
Po‑Hao Chen 0
0 National Pingtung University of Science and Technology , No. 1, Shuefu Rd., Neipu, Pingtung 912, Taiwan, ROC
Background: Cambial variations in lianas of Piperaceae in Taiwan have not been studied previously. The stem anatomy of seven Piper species from Taiwan was examined to document cambial variations and better distinguish the species when leaves are absent. Results: A key for the seven species is provided, based on the internal stem anatomy. The seven Piper species climb via adventitious roots, and in cross section, the stems were generally eccentric and oblate, although a transversely elliptic stem was found in P. kadsura (Choisy) Ohwi and P. sintenense Hatus. A cambial variant with secondary growth of external primary vascular bundles and xylem in plates was observed in all species except Piper betle L., which developed another cambium variant with xylem furrowed deeply by parenchyma proliferation. The sclerenchymatous ring surrounding the medullary vascular bundles was always continuous except in P. betle, where it was discontinuous. Mucilage canals varied from absent to present in the center of the pith, or present in the pith and inner cortex. Different sizes of vessels dispersed throughout the stem were ring or diffuse porous. The numbers of medullary and peripheral vascular bundles were distinctive and the widths of rays were noticeably different in each species. Differences in the growth rate of the medullary vascular bundles produced two development types of vascular bundles, although in both types, the peripheral vascular bundles gradually lengthen and become separated from each other by wide rays. Conclusions: We documented the internal stem anatomy of six previously unstudied species of Piper, including three endemic species, P. kwashoense Hayata, P. sintenense, and P. taiwanense Lin and Lu, and found that P. betle had deeply furrowed xylem, which had not been reported for the species before. The descriptions and photographs of seven Piper species will also provide a basis for further morphological studies.
Cortical vascular bundle; Liana; Mucilage canal; Piperaceae; Stem anatomy
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Background
Lianas usually have two stages of development, the
autologous support stage and the climbing stage (Schnitzer
and Bongers 2002). Internally, the autologous
support stage is characterized by a few narrow vessels and
many thick fibers. The climbing stage involves secondary
growth of the stem, which can be a standard or
anomalous (Isnard and Silk 2009). Morphological variation in
liana stems is primarily associated with the geometry of
the phloem and xylem, and irregular shapes within the
stems are classified into cambial variants (Angyalossy
et al. 2015). The diversity of liana stem shapes, structures,
and cambial variants has been recently reviewed
(Angyalossy et al. 2012), including those of Piperaceae.
Members of Piperaceae represent about five genera and
3700 species around the world (Christenhusz and Byng
2016), and many are economically important because
of their medicinal and culinary uses. They are erect or
scandent shrubs, small trees, or succulent, terrestrial
herbs, with nodose stems. The leaves are entire,
alternate to opposite or verticillate, petiolate or infrequently
subsessile, palmately nerved or penninerved, pellucid
dotted, and sometime aromatic (Souza et al. 2004). The
genus Piper L. is represented by about 1050 species
distributed primarily in the tropics (Mabberley 2008). The
most outstanding anatomical character in the Piperaceae
is the nature of the vascular bundles in the stem. In all
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species of Piperaceae studied to date in the genera Piper,
Manekia Trel., and Zippelia Blume, vascular bundles
are organized in two or more concentric rings, a
characteristic that is not present in other genera in Piperaceae
(Trueba et al. 2015).
Several studies have characterized cambial variants in
certain Piper species. Piper obtusilimbum C. DC. has a
typical arrangement of tissues (Tepe et al. 2007), with a
parenchymatous pith, medullary vascular bundles, a
sclerenchymatous cylinder, peripheral vascular bundles, and
a vascular cambium. The stem of Piper betle L. had an
inner irregular circle of primary vascular bundles
interspersed with a large mucilage canal in the pith, more
mucilage canals in the inner cortex, an undulating wall of
sclerenchyma, and an outer ring of smaller cortical
bundles. The primary vascular (medullary) bundles occupied
the pith (Beck 2011). Raman et (...truncated)