Development of the siphonous green alga Penicillus and the Espera state*

Abstract

The thallus of Penicillus is composed of two filament types: axial filaments of indeterminate growth and laterals of determinate growth. In vegetative reproduction new plants arise from horizontal rhizoids. Four stages can be distinguished in development. In the primordium stage the tip of a rhizoid swells and forms a primordium. In the germling stage ascending and descending axial filaments arise from the primordium, the former grow into a fascicle and give rise to lateral saccate branches, each of which forms an ascending and a descending arm and branches further into rhizoid‐like branchlets. Together these structures constitute the foundation of the stipe. At the same time the descending axial filaments elongate and become main rhizoidal filaments with lateral rhizoidal branchlets. In the early juvenile stage the stipe is formed. The elongating ascending axial filaments form a medulla while their laterals produce a cortex. In the late juvenile stage the axial filaments form the capitulum. The Espera state of Penicillus lacks a stipe since the ascending axial filaments do not join in a fascicle. Espera has been grown in laboratory cultures from Penicillus plants collected in the Caribbean region and also been found uncommonly in nature in this area. This state may be a response to environmental stress. The flattening of thalli and their orientation perpendicular to the direction of waves are discussed. A comparison of Penicillus and Codium indicates that at least two types of development exist in multiaxial Eusiphoniidae.

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“…In deeper water and where wave direction is more variable, such flattening is absent. These authors 3 note a similar phenomena in some species of Avrainvillea Decaisne, Udotea, and Halimeda. Such flattening may minimize destructive torsion (rotational) forces on wave exposed species, and encourage bending which reduces drag forces on these thalli.…”

“…However, given their demonstrated ability to grow and produce ramets once, it seems at least possible they could do so again if a ramet is lost; however, this may require continued attachment to a 'parent'. Penicillus, Rhipocephalus Kutzing, and Udotea also produce new thalli by such rhizoidal connections 6 , and in Penicillus the main form of reproduction is vegetative propagation by rhizoids 3 . While species of Caulerpa are unicellular like other coenocytes, many have internal elaborations (trabeculae), branched cell wall extensions that can span the diameter of the cell.…”

“…Thallus morphology and orientation of coenocytes is known to vary with the direction of the incoming waves 3 . In shallow water habitats, both the stipe and capitulum of Penicillus dumetosus (J.V.…”

New Mediterranean Marine biodiversity records (December, 2013)

“…The alga is composed of interwoven coenocytic filaments forming a rhizoidal base, a thin, rigid stripe, and a brush-like capitulum of free and dichotomously branched filaments (Friedman et al, 1977), the so-called "espera" stage. The "espera" stage is very rare in the Atlantic populations (Friedmann et al, 1977) while it is commonly found throughout the year in the Mediterranean Sea (Huve & Huve, 1964;Meinesz, 1972). The capitula of P. capitatus support large communities of macrofauna dominated numerically by small Crustaceans, mostly amphipods, tanaidaceans and large harpacticoid copepods (Stoner, 1985).…”

Penicillus capitatus: an algal island for macrocrustaceans

“…The calcareous green alga Penicillus capitatus Lamarck, found in shallow subtidal waters throughout the Caribbean Sea, the Bahamas, Florida and Bermuda (Taylor 1960), provides a convenient model for testing hypotheses related to island biogeographic processes. The alga is composed of interwoven coenocytic filaments forming a rhizoidal base, a thin, rigid stripe, and a brush-like capitulum of free and dichotomously branched filaments (Friedman & Roth 1977). The capitula of P. capitatus support large communities of macrofauna dominated numerically by small Crustacea, mostly amphipods, tanaidaceans and large harpacticoid copepods.…”