The Comparative Anatomy of Extrafloral Nectaries in the Cactus Family (Cactaceae)

Extrafloral nectaries (EFNs) are specialized glands that unlike floral nectaries, which function primarily in pollination, are typically associated with plant defense, attracting invertebrates whose presence and activity can reduce herbivory. EFNs were first observed in cacti in 1837 and have been noted in at least 25 different genera. Morphologically, cactus EFNs have been categorized as belonging to one of four distinct groups: short, obviously modified spines (type 1 EFNs); nectaries that resemble ordinary spines with no readily apparent modifications (type 2 EFNs); nectaries associated with small foliage leaves occurring adjacent to an areole (type 3 EFNs); and nectar-secreting regions of epidermis situated below an areole (type 4 EFNs). Although the distribution of these morphological types has been examined, little is known of their anatomical structure. My study refines this previous classification scheme characterizing type 1 EFNs as short, blunt projections consisting of a basal vascularized stalk filled with subnectary parenchyma and a broad secretory head containing layers of nectary parenchyma. Secretion appears to occur through ruptures in the cuticular covering of the gland. Type 1 EFNs are the most diverse group, with forms that range from spine-like, with an elongated secretory head containing fiber-like cells, to more specialized examples with flattened secretory heads that only contain isodiametric secretory cells. These EFNs can be phylogenetically informative on a species level within genera. In type 2 EFNs, nectar is produced in an area of small, isodiametric cells with dense cytoplasm at the base of a spine, then transported upwards to the sites of secretion. Type 3a and 3b EFNs secrete nectar from stomata in foliage leaves or modified leaf tissue. These stomata are located over subjacent vascular tissue with type 3a EFNs being associated with vegetative tissue and type 3b EFNs located on the exterior of pericarpel. Type 4 EFNs are also associated with leaf tissue but secrete nectar though open pits in patches of dark-red epidermis that are connected to subjacent vascular tissue.

Author dc:creator

• Burkholder, Jackson F.

Contributors dc:contributor

• Lemke, David E.
• Williamson, Paula S.
• Gorelick, Root

• cactus
• cacti
• nectary
• nectaries
• extrafloral nectaries
• extrafloral nectary
• plant secretion
• secretion
• secrertory tissue
• deserts
• americas
• cactaceae
• cacteae
• efn

Language dc:language

en

Identifier

Burkholder, J. F. (2024). The comparative anatomy of extrafloral nectaries in the cactus family (Cactaceae) [Master's thesis, Texas State University].

OAI identifier oai:identifier

oai:tdl-ir.tdl.org:10877/19296