Yang Sheng-Zehn, Chen Po-Hao
National Pingtung University of Science and Technology, No. 1, Shuefu Rd., Neipu, Pingtung, 912, Taiwan, ROC.
Bot Stud. 2017 Dec;58(1):17. doi: 10.1186/s40529-017-0172-z. Epub 2017 Mar 29.
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.
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.
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.
台湾胡椒科藤本植物的形成层变异此前尚未得到研究。对台湾七种胡椒属植物的茎解剖结构进行了研究，以记录形成层变异情况，并在无叶时更好地鉴别这些物种。
基于茎的内部解剖结构，给出了这七个物种的检索表。这七种胡椒属植物通过不定根攀爬，横切面上，茎通常为偏心扁圆形，不过在台东胡椒（Piper kadsura (Choisy) Ohwi）和台东土楠胡椒（Piper sintenense Hatus）中发现有横椭圆形的茎。除了蒌叶胡椒（Piper betle L.）外，在所有物种中均观察到一种形成层变异类型，其外部初生维管束和木质部呈板状进行次生生长，而蒌叶胡椒则发育出另一种形成层变异类型，其木质部因薄壁组织增生而有深深的沟纹。围绕髓部维管束的厚壁组织环除蒌叶胡椒外总是连续的，在蒌叶胡椒中是不连续的。黏液道在髓部中心有的没有，有的有，或者在髓部和内皮层中存在。分布于整个茎中的不同大小的导管为环孔或散孔。每个物种的髓部和外围维管束数量不同，射线宽度也明显不同。髓部维管束生长速率的差异产生了两种维管束发育类型，不过在这两种类型中，外围维管束都会逐渐延长，并被宽射线彼此分开。
我们记录了六种此前未被研究过的胡椒属植物的茎内部解剖结构，包括三种特有物种，即台湾胡椒（Piper kwashoense Hayata）、台东土楠胡椒和台湾胡椒（Piper taiwanense Lin and Lu），并发现蒌叶胡椒有深深沟纹的木质部，此前该物种未曾有过这样的报道。这七种胡椒属植物的描述和照片也将为进一步的形态学研究提供基础。
