The structure of the paracladial zone in Poaceae

Abstract

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Ontogeny and structure of the acervulate partial inflorescence in Hyophorbe lagenicaulis (Arecaceae; Arecoideae)

“…Moreover, apart from the study describing selected developmental stages of acervuli in Hyophorbe indica (Uhl and Moore, 1978), relatively few data have been obtained on the ontogeny of this type of partial inflorescence. Two major elements have traditionally made the acervulus a difficult subject to study: (1) the lack of obvious pherophylls (subtending bracts) for individual flowers, as already reported in plant families such as the Brassicaceae (Hagemann, 1963), Papilionoideae (Prenner, 2004), Poaceae (Vegetti and Weberling, 1996), Araceae (Buzgo, 2001), Hydatellaceae (Rudall et al, 2007) and Nympheaceae (Endress and Doyle, 2009), has strongly hindered the interpretation of the general architecture of the acervulus; (2) the basipetal direction of development displayed by the acervulus differs from the acropetal ontogenetic progression seen in its architecture, leading to equivocal interpretations with respect to its origin and, hence, to its type of branching system. The apparent structural contradiction between the two types of partial inflorescences occurring in the Arecoideae (floral triad vs. acervulus) has prompted us to undertake the first complete ontogenetic study of the acervulus in a member of the tribe Chamaedoreeae (Hyophorbe lagenicaulis), in order to better understand its specific developmental pattern.…”

Inflorescence Structure

“…In many grasses, it is possible to identify three zones or parts of the plant in which axillary buds have different fates. The lowest zone is described as the "innovation zone" (Vegetti and Weberling 1996), in which buds from the lowest nodes on the plant can produce tillers that reiterate the structure of the primary axis. Above this is an area called the "zone of inhibition" in which axillary buds generally do not elongate at all (Vegetti and Weberling 1996).…”

“…The lowest zone is described as the "innovation zone" (Vegetti and Weberling 1996), in which buds from the lowest nodes on the plant can produce tillers that reiterate the structure of the primary axis. Above this is an area called the "zone of inhibition" in which axillary buds generally do not elongate at all (Vegetti and Weberling 1996). The upper part of the plant is then the "paracladial zone" (Vegetti 1991;Vegetti and Anton 1996) in which axillary buds can grow out and produce paraclades, inflorescences whose structure is indistinguishable from that of the terminal inflorescence.…”

Types of enrichment axes in Poaceae

“…The enrichment axes originating in the distal region of the LIZ normally present a prophyll and developed leaves (trophotagma) (Rua and Weberling, 1998;Vegetti and Weberling, 1996) and terminate in an UIF similar to that of the relative mother axis that supports them. These axes have been denominated paraclades of the trophotagma (Vegetti and Müller-Doblies, 2004), long paraclades of second order (Weberling et al, 1993) or paraclades with trophotagma (Vegetti and Weberling, 1996).…”

“…These axes have been denominated paraclades of the trophotagma (Vegetti and Müller-Doblies, 2004), long paraclades of second order (Weberling et al, 1993) or paraclades with trophotagma (Vegetti and Weberling, 1996). From the axillary buds of the trophotagma of these enrichment axes, new axes of similar structure can be originated.…”