Dictyotales (from Greek diktyotos 'netlike')[2] is a large order in the brown algae (class Phaeophyceae) containing the single family Dictyotaceae. Members of this order generally prefer warmer (tropical to subtropical) waters than other brown algae, and are prevalent in tropical and subtropical waters thanks to their many chemical defenses to ward off grazers. They display an isomorphichaplodiploid life cycle and are characterized by vegetative growth through a single apical cell. One genus in this order, Padina, is the only calcareous member of the brown algae.[3]
Dictyotales are composed of flattened, parenchymatousthalli. They display apical growth: a single apical cell forms the flattened thallus, the vegetative part of the organism, through mitosis. The mature thallus is composed of three layers: one middle layer of large cells lacking chloroplasts, surrounded by two layers of small cells packed densely with chloroplasts[4] lacking pyrenoids. Some taxa exhibit blue-green iridescence when submerged. Some species of Dictyopteris and Spatoglossum have cellular vacuoles with very low pH (between 0.5 and 0.9).[2]
The female sori, deep-brown in color, usually have 25–50 oogonia, with sterile oogonia localized at the margin. To develop an oogonium, a surface cell divides into a stalk cell and the oogonium proper. Each oogonium produces one egg cell that is released through a gelatinized apex in its wall.[4]
The male sori, resembling white glistening spots, are surrounded by elongated sterile cells regarded as undeveloped antheridia. They can be recognized early in their development due to the disintegration of chloroplasts in their cells. To develop an antheridium, the surface cells enlarge and divide horizontally into a stalk cell and a primary spermatogenous cell, which in turn divides vertically and horizontally into 650–1500 compartments or locules, each producing one sperm cell. Each sperm cell is pear-shaped, with an anterior eyespot and only one flagellum inserted laterally, although two basal bodies are present, indicating an origin from a biflagellate ancestor. They are released from the antheridium through dissolution of the walls.[4]
The egg cell secretes a pheromone, dictyotene, to attract the sperm cell. After the fertilization between the two gametes, the resulting diploidzygote grows into the sporophyte generation. On their surface, modified sporangia typically produce through meiosis four haploid non-flagellated aplanospores, but a few genera produce eight spores per sporangium (Lobophora, Zonaria) or flagellated spores (Exallosorus), two features considered primitive.[5] The spores, while naked are released through the gelatinized apex of the sporangium. Soon after, they grow a cellulosewall and grow into gametophytes.[4]
Dictyotales are most diverse in tropical and subtropical waters, but extend into temperate regions.[2] They are one of the few brown algal orders whose species can form a conspicuous, even dominant component of tropical and temperate marine floras. Their ecological success is often linked to their ability to deter grazers in habitats subject to strong grazing pressure, making them an important competitor of corals and other sessile benthic life in many coastal ecosystems.[5] Some species, in particular within the genus Dictyota, produce terpenoids (such as pachydictyol) that inhibit grazing by herbivorousamphipods, sea urchins and fish.[4] The species Lobophora variegata produces a cyclic lactone, lobophorolide, that in low concentrations is an active compound against pathogenic and saprophyticmarine fungi.[2]
Dictyotales contains the only calcareous genus of brown algae, Padina. Its margins contain a layer of apical cells with hairs that create a microenvironment where aragonitenucleation occurs, if isolated from the water flow.[4]
The latest revision of brown algae, published in 2014, recognizes 19 genera within Dictyotales, as well as 7 genera that have been synonymized with the accepted genera.[1]
CanistrocarpusDe Paula & De Clerck in De Clerck et al., 2006
^ abcDe Clerck O, Leliaert F, Verbruggen H, Lane CE, De Paula JC, Payo DA, Coppejans E (2006). "A revised classification of the Dictyoteae (Dictyotales, Phaeophyceae) based on rbcL and 26S ribosomal DNA sequence analyses". Journal of Phycology. 42: 1271–1288. doi:10.1111/j.1529-8817.2006.00279.x.
^Bittner L, Payri CE, Couloux A, Cruaud C, de Reviers B, Rousseau F (2008). "Molecular phylogeny of the Dictyotales and their position within the Phaeophyceae, based on nuclear, plastid and mitochondrial DNA sequence data". Molecular Phylogenetics and Evolution. 49 (1): 211–226. doi:10.1016/j.ympev.2008.06.018.
Gauna, Cecilia; Caceres, Eduardo; Parodi, Elisa (December 2013). "Temporal variations of vegetative features, sex ratios and reproductive phenology in a Dictyota dichotoma (Dictyotales, Phaeophyceae) population of Argentina". Helgoland Marine Research. 64 (4): 721–732. doi:10.1007/s10152-013-0357-0.
Lozano-Orozco, Jorge G.; Sentíes, Abel; Díaz-Larrea, Jhoana; Pedroche, Francisco F.; de Clerck, Olivier (1 January 2014). "The occurrence of Dictyota canariensis (Dictyotales, Phaeophyceae) in the Gulf of Mexico". Botanica Marina. 57 (5): 359–365. doi:10.1515/bot-2013-0111.
