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Abstract Detail


Developmental and Structural Section

Posluszny, U [1], Tomlinson, P. Barry [2].

Shoot organization in the seagrass Halophila (Hydrocharitaceae): The evolution of modular construction in an early monocotyledon.

Thirteen genera within the Alismatidae can be characterized as seagrasses. The genus Halophila is amongst the most ubiquitous and cosmopolitan of the seagrasses being found in just about every tropical ocean. There are approximately 12 species in this genus divided into five sections. Subdivision of the genus is based on the organization of the “modular” erect shoot and position of flowers. Branching throughout is precocious and always occurs above the insertion of the youngest appendage as a terminal bifurcation. It may be described as monopodial because the lateral (erect) axis is distinct from the horizontal parent (rhizome) axis in producing foliage leaves. Terminal buds of the rhizome are distinguished by the large number of appendages that may be enclosed in the enveloping pair of scale leaves, with up to eight visible branch orders. Despite the high degree of preformation and apparent continuous growths, there seems to be some overall control of meristem development such that only a few of the apices are activated. All of the erect shoots become floral. The small heterochronic shifts that occur in the development of the erect shoots are enough to produce the five different modular forms that are diagnostic of the sections within this genus.

Broader Impacts:
Rhizomatous branching, common in many monocotyledons, is a good example of how plants can efficiently exploit terrestrial and aquatic ecosystems. One could speculate that the flexible and modular nature of rhizomes played an important role in the evolution of seagrasses. It might even lead to a plausible explanation of why only members of the monocotyledons have adapted to a marine environment. Halophila with a dimorphic shoot system and a highly compact precocious rhizome tip is a perfect example of a successful seagrass genus.


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1 - University of Guelph, Molecular and Cellular Biology, Guelph, Ontario, N1G 2W1, Canada
2 - Harvard University, Harvard Forest, Po Box 68, Petersham, Massachusetts, 01366, USA

Keywords:
Halophila
Hydrocharitaceae
seagrasses
marine
rhizomes
branching
shoots.

Presentation Type: Oral Paper:Papers for Sections
Session: 51
Location: 555B/Convention Center
Date: Wednesday, August 4th, 2010
Time: 11:30 AM
Number: 51014
Abstract ID:121


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