Rhodophyta, Red Algae
Asparagopsis taxiformis (Delile) Trevisan
Rhodophyta, Order: Bonnemaisoniales; Family: Bonnemaisoniaceae.
Asparagopsis refers to its resemblance to the asparagus plant. The name of the species -taxiformis -refers to the arrangement of its branches, which resembles that of the Yew tree.
The Asparagopsis taxiformis is a very soft alga that loses its shape when extracted from the water. The central axis is covered with irregular lateral fissures 1 cm in diameter at the base and several millimetres at the tip. The fissures are arranged in a pyramid form - sharpened at the end. The algal cling is made of several crawling shoots that attach to a substrate using a wedge-like rhizoid, often forming a thicket at the base of the colony. Microscopic examination reveals 2 rows of cells along the side branches.
The Asparagopsis taxiformis is between 5 to 20 cm long (very rarely - 30 cm), but most are in the 10 cm region. The side branches (the algal diameter) varies between several millimeters to a centimeter (a 2 cm diameter is rare).
The Asparagopsis taxiformis comes in shades of pink, veering towards gray or very light brown. Usually, the algal base is pinker and its top grayish.
The Asparagopsis taxiformis is found in dense colonies, coloured pinkish-brown, and characterized by its soft thallus and pyramid shape. It may be confused with Dasya plants, but that plant’s characteristic pompoms are missing, and it is very rare.
Rocky beaches of the Eastern Mediterranean are where the Asparagopsis taxiformis grows attached to the substrate, creating dense colonies in the upper region of the subtidal zone, in areas that are never exposed. In literature, the Asparagopsis taxiformis has been reported at depths of 15 to 30 m. In Australia and other places, the alga is considered an epiphyte, and it apparently also grows on ships, which transport it from one place to another.
Biology and reproduction
The Asparagopsis taxiformis three staged life cycle includes a gametophytic stage (described below) and a sporophytic stage. The algal gametophyte holds in the base of its branches round, but sometimes elongated, sporangia whose diameter may be 1 mm, but they are usually smaller. The sporophytic branches resemble a bundle of hairs, have elongated sporangium bodies, are usually located in the top of central branches and resemble the branches of the Polysiphonia alga. Microscopic examination from above reveals filaments containing 2 rows of cells, sharpened at the edges and irregularly branched. The holdfast is disk- like. The sporophytic branches grow to 2 cm in length and are pinkish-red coloured. Not all stages of the life cycle have been observed in all those places where the alga has been reported, and the sporophytic stage may also be able to reproduce by fragmentation.
Seasonality and distribution
The Asparagopsis taxiformis is rare in this region. I myself have only seen it twice along Israeli shores: in Mikhmoret, where it was also reported by Dr. Lundberg, and at the Neve Yam beach (Israel). The species has also been reported in Egypt by its previous name -Asparagopsis delilei Montagne. The algal tropical and sub-tropical distribution is wide, arriving in Europe at the beginning of the twentieth century, probably by ship.
The Asparagopsis genus includes two species, but only one of them, the Asparagopsis taxiformis, has so far been reported in our region. The other species is only known to exist in Australia and New Zealand.
The algal sporophytic stage was erroneously considered a separate species - the Polysiphonia hillebrandii Bornet until 1961, and as the Falkenbergia hillebrandii (Bornet) Falkenberg thereafter.
Asparagopsis taxiformis, on the right: procarp, on the left: cistocarp - an asexual structure developed as a parasite in the female sporophyte.
Asparagopsis taxiformis -a general view of the cellular arrangement at the edge of the holdfast, from which several rhizoids branch out.
In the Caribbean Islands, the Asparagopsis taxiformis is a popular consumable, used as a spice and a common addition to fish and meat dishes.