A Note on the Structural Peculiarities of the Leaves of Amentotaxus formosana Li in Southern Taiwan

The relic endemic species, Amentotaxus formosana Li, was evaluated as having an endangered (EN) status in the Red List of Vascular Plants of Taiwan. Its populations have a limited geographic distribution in broadleaf forests at elevations of 800 to 1400 m in the southern Central Mountain Range of Taiwan. Genetic variations, genetic divergence, and DNA barcoding all pointed out that well-differentiated species need to be preserved, but scant evaluations have been conducted of the environmental impacts of its traits for conservation purposes. Our results are the first report on anatomical peculiarities of leaf traits of A. formosana, such as the leaf vascular cambium, transfusion tracheids, a thick outer cuticle layer on both sides of the epidermis, the actinocytic type of stoma complex with an arrangement of six to eight subsidiary cells, mostly two-cell distances among stomata, and no stomata being distributed in clusters. The leaf vascular cambium which is rarely found in gymnosperms produces secondary vascular tissues which are enclosed inside thick-walled bundle sheath cells with dense phenolic contents. Transfusion extensions with elongated sclerenchyma tangles provide auxiliary support from the midrib to the broad leaf blade. These peculiar transfusion extensions run from the bundle sheath or transfusion tissue in a sideways direction instead of up-and-down, perpendicular to the leaf surface, and differ from the bundle sheath extensions. It indicates important structural and functional roles for stretching out from the leaf vasculature. The occurrence of the leaf vascular cambium indicates long-lived functions in water supply and long-term photosynthate assemblages, a trade-off between a thick cuticle layer and dramatically large stomata areas of the leaf in this species for managing water loss in a foggy, humid environment accompanied by the impact of sudden drought by foehn winds in the sprouting season. All above should be considered when elucidating strategies from conservation perspectives.

關鍵字

leaf vascular cambium ； transfusion tissue ； transfusion extension ； bundle sheath ； stomatal complex

並列摘要

臺灣穗花杉（Amentotaxus formosana Li）為臺灣維管束植物紅皮書評估為瀕危（endangered, EN）的特有物種，地理分布侷限臺灣中央山脈南部海拔800至1400公尺的闊葉林內。遺傳變異、遺傳差異和DNA條碼都指出此分化完全的物種需要保護，但很少對保護區環境壓縮的特性進行評估。我們的研究結果是關於臺灣穗花杉葉性狀解剖學特徵的首次報導：葉維管束形成層，轉輸管胞組織，表皮上下側的外角質層較厚，氣孔複合體（或稱氣孔器）具有6至8個副細胞的放射型排列，大多數氣孔之間是2個表皮細胞間距，以及氣孔無成簇分佈的現象。極少在裸子植物中可發現，葉具有維管束形成層且產生次生維管束組織，此被具有高濃含量酚類的厚壁束鞘細胞所圍住。轉輸組織延伸具有細長的厚壁組織纏結，作為從中脈到寬的葉身的支撐輔助力量。這種特殊的轉輸組織延伸從束鞘或轉輸組織，以側向、而不是上下垂直於葉面的方向延伸，與束鞘延伸組織不同，顯示從葉脈維管束系統伸展出在結構和功能中扮演重要的作用。葉片維管形成層的出現在供水和長期光合作用合成中具有長壽命、長效功能，在該物種厚厚的角質層和葉片大面積的氣孔帶之間進行權衡，藉以管理欠缺敏感環境中的水分流失，以及發芽季節時焚風的影響，以上結果可能會激發保育策略的新觀點。

並列關鍵字

葉維管束形成層；轉輸組織；轉輸組織延伸；維管束鞘；氣孔器

主題瀏覽