Red de Ecología Funcional, Instituto de Ecología, A.C., Carretera antigua a Coatepec No. 351, El Haya, Xalapa, 91073, México.
Institute of Systematic Botany and Ecology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany.
Am J Bot. 2022 Jan;109(1):46-57. doi: 10.1002/ajb2.1781. Epub 2022 Jan 7.
Extrafloral nectaries have mainly been studied in angiosperms, but have also been reported in 39 fern species. Here we provide a global review of nectaries in ferns and examined their structure, function, and nectar sugar composition in two genera.
We searched in the literature and living plant collections of botanical gardens for indications of fern nectaries, observed nectar-feeding animals, studied the morphoanatomy in the two genera Aglaomorpha and Campyloneurum, and analyzed the total sugar concentrations and ratios of 16 species. Diurnal nectar release was observed with time-lapse photography.
We found evidence for nectaries in 101 species of ferns from 11 genera and 6 families. Most of the nectary-bearing species were tree ferns (Cyatheaceae) and epiphytic ferns of the family Polypodiaceae. Nectaries consisted of cytoplasm-rich parenchyma with large nuclei and an epidermis with or without stomata, were attached to amphiphloic vascular bundles, and released nectar on the lower leaf surface mainly on expanding leaves during the night. Sugar concentrations varied between species (3.8-15.3%) but not between genera, and were sucrose-dominant (3 spp.), sucrose-rich (7), or hexose-rich (3). In the greenhouse, introduced ants, scale insects, and snails fed on the nectar.
The wide taxonomic distribution, variable morphology, locations, and sugar compositions point to multiple evolutionary origins of fern nectaries. Nectar release in young leaves might attract mutualistic ants to protect leaves against herbivores only during this most vulnerable developmental stage. Even ex-situ, fern nectar is a valuable food source because it attracted several opportunistic animal species.
花外蜜腺主要在被子植物中进行研究，但也在 39 种蕨类植物中报道过。在这里，我们对蕨类植物中的蜜腺进行了全球综述，并检查了两个属的结构、功能和花蜜糖组成。
我们在文献和植物园的活体植物收藏中搜索蕨类植物蜜腺的迹象，观察花蜜取食动物，研究两个属 Aglaomorpha 和 Campyloneurum 的形态解剖结构，并分析 16 个物种的总糖浓度和比例。使用延时摄影观察白天的花蜜释放。
我们在 11 个属和 6 个科的 101 种蕨类植物中发现了蜜腺的证据。大多数有蜜腺的物种是树蕨（Cyatheaceae）和附生蕨类 Polypodiaceae。蜜腺由富含细胞质的薄壁组织组成，具有大核和具有或不具有气孔的表皮，附着在两栖血管束上，主要在夜间通过展开的叶子从下叶面释放花蜜。糖浓度在物种之间变化（3.8-15.3%），但在属之间不变，且以蔗糖为主（3 种）、蔗糖丰富（7 种）或己糖丰富（3 种）。在温室中，引入的蚂蚁、介壳虫和蜗牛以花蜜为食。
广泛的分类分布、可变的形态、位置和糖组成表明蕨类植物蜜腺有多种进化起源。在最脆弱的发育阶段，幼叶中花蜜的释放可能会吸引互惠互利的蚂蚁来保护叶子免受食草动物的侵害。即使在非自然环境中，蕨类植物花蜜也是一种有价值的食物来源，因为它吸引了几种机会主义动物物种。
