File:Gracilaria tikvahiae (graceful redweed) (Cayo Costa Island, Florida, USA) 1 (23689886804).jpg

Gracilaria tikvahiae McLachlan, 1979 - graceful redweed in Florida, USA (January 2016).

Rhodophytes are red algae - they are the most common and widespread of marine macroalgae, but they often go unnoticed because of their frequently-dull coloration and nondescript growth forms.

About 4000 species of red algae are known in the Holocene - most of them are marine, plus some freshwater forms. Rhodophytes are known in the fossil record. The oldest reported fossil red algae are from the upper Mesoproterozoic (~1.2 Ga) of northern Canada.

Red algae vary in coloration - not all are reddish-colored. Rhodophytes can be red, pink, pale pinke, lavender, purple, brownish-red, whitish, and yellowish. Fleshy red algae are usually weed-like to mossy to fuzzy in appearance. Calcareous red algae have skeletons with calcium carbonate (CaCO3 - calcite or aragonite). Calcareous red algae are important reef organisms - they include branching forms and crusts. Upon death, the hard part skeletal components of calcareous red algae become biogenic sediments in reef and peri-reef environments.

Gracilaria tikvahiae is a common species of fleshy red alga that occurs in the western North Atlantic Ocean (= eastern coastal areas of Canada & America) and the Gulf of Mexico (Florida to Mexico).

Classification: Rhodophyta, Rhodophyceae, Gigartinales (or Gracilariales), Gracilariaceae

Locality: high tide strand line on marine beach at the southern tip of Cayo Costa Island, Gulf of Mexico coast of southwestern Florida, USA (vicinity of 26° 36' 48.74" North latitude, 82° 13' 19.91" West longitude)

More info. at: en.wikipedia.org/wiki/Red_algae and en.wikipedia.org/wiki/Gracilaria and www.sms.si.edu/irlspec/Gracil_tikvah.htm and