Abstract
An enigmatic feature of tropical pitcher plants belonging to the genus Nepenthes is their dimorphic prey-capturing pitfall traps. In many species, the conspicuously shaped upper and lower pitchers grow from a swollen leaf tendril tip until finally opening as insect-alluring devices. Few have studied the ontogeny of these traps from an anatomical and quantitative morphological perspective. We investigated whether the anatomy and development of lower and upper type pitchers of N. rafflesiana differ or overlap in terms of 3D geometric morphology and microstructure progression and presence. We hypothesized that there is an overlap in the initial, but not all, developmental stages of the two pitcher types and that one pitcher type is suspended in development. We identified four important morphological changes of pitcher ontogeny and defined these as curvation, elongation, inflation and maturation phases. Pitcher length indicated progress through developmental phases, and we propose to use it as a tool for indication of developmental stage. Microstructure development coincided with the developmental phases defined. Additionally, we discovered a new anatomical feature of extrafloral nectariferous peristomal glands between the inner peristome ridges of upper and lower pitchers being hollow and analyze the chemistry of the sugars on the outside of these glands. Ontogenetic shape analysis indicated that upper and lower pitcher types develop with similar phase progression but have no directly overlapping morphology. This means that upper pitchers are not a derived state from lower pitchers. Independent developmental programs evolved to produce distinctly shaped upper and lower pitchers in Nepenthes, likely to exploit different food sources.
Highlights
The tropical carnivorous plant genus Nepenthes is characterized by one of the most striking morphological features of plants: an insect-luring pitfall trap
The first developmental phase begins when pitchers are first distinguishable as a swollen tendril tip, which extends from the midvein of the blade-like leaf (Figure 1A)
Phases identified during traditional morphometric analysis led our investigation of microstructure development through Scanning Electronic Microscopy (SEM) and Light
Summary
The tropical carnivorous plant genus Nepenthes is characterized by one of the most striking morphological features of plants: an insect-luring pitfall trap These traps, modified leaf tips called pitchers, are an adaptation to scarcity of nutrient resources and facilitate the capture of an abundant nitrogen alternative [1,2]. Throughout their distribution region in the Malay Archipelago, Australia, India, and Madagascar [3,4], the 140+ recognized species [5] attract insects, such as flies, ants, or termites, through visual lures [6,7], extrafloral nectar [8,9,10], and olfactory cues [11]. The single detritivore described, Nepenthes ampullaria, has an open-mouth that is largely reduced compared to other species and is associated with leaf-litter accumulations [31,32]
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