Stpiczyńska Małgorzata, Pansarin Emerson R, Davies Kevin L, Płachno Bartosz J, Wrazidlo Mateusz, Stodolska Klaudia, Czortek Patryk
Faculty of Biology, University of Warsaw, Botanic Garden, Al. Ujazdowskie 4, Warsaw, 00-478, Poland.
Department of Biology, University of São Paulo, FFCLRP, Ribeirão Preto, SP, Brazil.
BMC Plant Biol. 2025 Jun 7;25(1):772. doi: 10.1186/s12870-025-06810-5.
The orchid subtribe Laeliinae has an assemblage of morphologically diverse taxa. The diversity in floral morphology of its members can be explained in terms of pollination ecology in that this subtribe contains both entomophilous and ornithophilous species. Given the wide range of pollinators, one would expect to find considerable differences in morphology of the floral nectaries. Fully developed nectaries appeared to be entirely non-functional in some taxa. The aim of this work was to compare the micromorphology of the inner nectary spur in selected representatives of Laeliinae in order to ascertain which structural features improve or reduce nectar secretion, and thereby contribute towards the evolutionary success of this subtribe. Here, we investigate the nectary structure of 48 species representing the genera Prosthechea, Encyclia, Epidendrum and Dinema. Of these, the nectary of Encyclia was of the narrow-tubular form (cuniculus-type), that of Prosthechea and Dinema was short and sac-like, whereas both nectary types were present in Epidendrum, the former type being the more common. Whereas the nectary of Dinema contained nectar, this was either absent or present in nectaries of the other three genera. Statistical analyses of the morphological and micromorphological characters of the nectary revealed that the probability of nectar being present was lower for the long, tubular nectaries (e.g. Encyclia and Epidendrum), whereas most Prosthechea spp. investigated, as well as Dinema, possessed sac-like, functional nectaries. Also, all investigated taxa, irrespective of the presence of nectar, shared a thick cuticle and thick epidermal and subepidermal cell walls (in the secretory layer). Analyses also showed that the probability of nectar being present increased with an increase in the thickness of the secretory layer. Furthermore, there was also a greater probability of the epidermal cells lining functional nectaries having a smooth cuticle. The occurrence, or otherwise, of nectar may indicate that the secretory capacity of this group of orchids is plastic, and not limited by structural constraints, thus allowing for the relatively easy turning on and off of the secretory process.
树兰亚族拥有一系列形态多样的分类群。其成员花形态的多样性可以从传粉生态学的角度来解释，因为这个亚族既包含虫媒传粉的物种，也包含鸟媒传粉的物种。鉴于传粉者种类繁多，人们预计会在花蜜腺的形态上发现相当大的差异。在一些分类群中，发育完全的花蜜腺似乎完全没有功能。这项工作的目的是比较树兰亚族选定代表植物中内花蜜距的微观形态，以确定哪些结构特征会促进或减少花蜜分泌，从而有助于该亚族的进化成功。在这里，我们研究了代表扁轴兰属、毛唇兰属、树兰属和筒距兰属的48个物种的花蜜腺结构。其中，毛唇兰属的花蜜腺呈窄管状（沟状），扁轴兰属和筒距兰属的花蜜腺短且呈囊状，而树兰属则同时存在这两种花蜜腺类型，前一种类型更为常见。筒距兰属的花蜜腺含有花蜜，而其他三个属的花蜜腺中要么没有花蜜，要么有花蜜。对花蜜腺的形态和微观形态特征进行统计分析表明，长管状花蜜腺（如毛唇兰属和树兰属）存在花蜜的概率较低，而大多数被研究的扁轴兰属物种以及筒距兰属都拥有囊状的、有功能的花蜜腺。此外，所有被研究的分类群，无论是否有花蜜，都有一层厚厚的角质层以及厚厚的表皮和皮下细胞壁（在分泌层）。分析还表明，随着分泌层厚度的增加，存在花蜜的概率也会增加。此外，有功能的花蜜腺内衬的表皮细胞具有光滑角质层的概率也更高。花蜜的有无可能表明这组兰花的分泌能力具有可塑性，不受结构限制，从而使得分泌过程相对容易开启和关闭。
