Nectary structure and nectar in Sobralia and Elleanthus (Sobralieae: Orchidaceae)

With approximately 200 species, the tribe Sobralieae is a dominant and common Neotropical group of orchids, yet little is known of variation in floral morphology as it relates to their pollination. As currently circumscribed, the tribe includes four genera that differ considerably in flower size and morphology: Elleanthus, Epilyna, Sertifera, and Sobralia. Although nectar-foraging pollinators are known for some species, the relationships of pollination to deceit and to nectar production are all poorly understood. We examined pollination-related of nectaries and nectar characteristics (presence/absence, volume, and concentration) for major clades of Sobralieae. Some species produce abundant nectar, but many species offer no reward. When present, nectar is secreted by thickened calli at the lip base. The cells of the nectariferous calli contain starch, which is rapidly converted to sugar during a brief anthesis (often lasting only one day). Most Sobralia flowers are relatively large, bee-pollinated, with a gullet-shaped lip, false nectary, large pollinia, and offer no reward. Elleanthus flowers are relatively small with a legitimate nectar reward, and most species are hummingbird- pollinated. Hummingbird-pollinated Sobralieae flowers are relatively small, brightly colored in the perianth and/or the subtending bracts, somewhat tubular, with a lip that forms a cup around the callus for storing nectar, and pollinia that are dark and relatively small.

Structure of floral nectaries, nectar production and sugar composition in nectar of 7 species of Vicia L. Fabaceae

Nectaries of investigated species of <em>Vicia</em> were ranked into 3 morphological types: automorphic (<em>V. sepium</em> L.), transitoric (<em>V. angustifolia</em> L., <em>V. sativa</em> L., <em>V. villosa</em> Roth, <em>V. cracca</em> L.) and flat, epimorphic (<em>V. hirsuta</em> (L.) S. F. Gray and <em>V. tetrasperma</em> (L.) Schreb.). The best nectaring was connected with well defined nectary structure, and moreover quantity of nectar was correlated with nectary size but was not depended on number of secretory stomata. Sucrose dominated in the nectar of 6 species of vetches, the exception was balanced nectar of <em>V. tetrasperma</em>.

"Sweet but dangerous": nectaries in carnivorous plants

In carnivorous plants, two types of nectaries occur: extra-floral nectaries, generally associated with prey luring, and floral ones associated with pollination. Nectar produced by extra-floral nectaries not only attracts prey but may also be involved in trapping prey and plays a role in myrmecophily. The diversity of nectary structure in carnivorous plants reflects complicated evolutionary routes in this unique ecological group.

Nectary structure in Symphyglossum sanguineum (Rchb.f. ) Schltr. (Orchidaceae)

Ornithophily occurs in a great number of orchid species but despite this, researchers have largely neglected to investigate their nectaries. The aim of this study is to describe the nectary structure of <i>Symphyglossum sanguineum</i>, a species presumed to be pollinated by hummingbirds. The nectary is located at the free margins of auricles, which form a channel for the passage of nectar. The nectary, which consists of a single-layered epidermis and 2-3 layers of subepidermal cells, is supplied by collateral, vascular bundles. The nectary cells of <i>S. sanguineum</i>, like those of other ornithophilous orchids, have thick cellulose cell walls. A remarkable feature of these nectary cells is the dissolution of the middle lamella and the subsequent separation of epidermal cells. It is possible that this latter process facilitates the flow of the nectar to the nectary surface. The cuticle covering the nectary epidermis has micro-channels, but unlike the other species of ornithophilous orchids studied to date, it neither becomes disrupted nor detached from the epidermal cells. Abundant mitochondria, lipid droplets and smooth endoplasmic reticulum (SER) with an osmiophilic material are present in the cytoplasm of nectary cells. Some plastids with few lamellae contain numerous vesicles and osmiophillic globules whereas others accumulate starch. SER lamellae are often closely associated with plastids and the contents of the former organelles closely resemble osmiophillic globules. Secretory vesicles are common, especially near the outer, tangential wall indicating that granulocrine secretion possibly occurs in <i>S. sanguineum</i>.

Nectary structure of Ornithidium sophronitis Rchb.F. (Orchidaceae: Maxillariinae)

Most orchids do not produce floral food-rewards. Instead, they attract pollinators by mimicry or deceit. When present, the most common floral food-reward is nectar. To date, nectary structure has been described for only two species of <i>Maxillaria sensu lato</i>, namely <i>Maxillariella anceps</i> and <i>Ornithidium coccineum</i> (formerly <i>Maxillaria anceps</i> and <i>M. coccinea</i>, respectively). Here, we describe that of a third species, <i>Ornithidium sophronitis</i> (formerly <i>Maxillaria sophronitis</i>). This species possesses floral characters concomitant with ornithophily. A 'faucet and sink' arrangement is present, with nectar secreted by a protuberance on the ventral surface of the column, collecting between column and tepal bases. The nectary of <i>O. sophronitis</i> shares many features with that of <i>O. coccineum</i>. It has a single-layered epidermis and 3- 5 layers of small, subepidermal, collenchymatous, secretory cells. Beneath these occur 2-3 layers of larger, subsecretory, parenchymatous cells supplied by phloem. Nectary cell vacuoles contain osmiophilic material and proteinaceous intravacuolar bodies. Moreover, distension of the nectary cuticle occurs as nectar accumulates between it and the secretory epidermis. Subsecretory cells, however, have thinner walls and contain flocculent, intravacuolar precipitates that may be related to the presence of flavonoids. Since the floral and nectary structure of <i>O. sophronitis</i> is very similar to that of closely related <i>Ornithidium coccineum</i>, it may have evolved in like manner in response to similar pollinator pressures.