Cambial variations of Piper (Piperaceae) in Taiwan

Sheng-Zehn Yang,Po-Hao Chen

doi:10.1186/s40529-017-0172-z

Sheng-Zehn Yang, Po-Hao Chen

Open Access

https://doi.org/10.1186/s40529-017-0172-z

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Abstract

BackgroundCambial 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.ResultsA 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.ConclusionsWe 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.

Highlights

Cambial variations in lianas of Piperaceae in Taiwan have not been studied previously
The number of medullary vascular bundles or peripheral vascular bundles varied among species, from approximately 4–7 medullary vascular bundles in P. sintenense (Fig. 1g) to 12–19 in P. betle (Fig. 1b, c) and approximately 15–23 peripheral vascular bundles in P. kadsura (Fig. 1d) and P. sintenense (Fig. 1g) to 34–41 in P. kwashoense (Fig. 1f )
The medullary vascular bundles persist but their growth is eventually minimal, while the peripheral vascular bundles continue to develop as the stem increases in diameter, and secondary thickening is restricted to the peripheral vascular bundles (Fig. 2a–d) due to the fascicular cambia that are located between the phloem and xylem of the peripheral vascular bundles

Summary

Introduction

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. 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). 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.

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