Rhea (bird) Rhea (bird) The rheas () are large ratites (flightless birds without a keel on their sternum bone) in the order Rheiformes, native to South America, distantly related to the ostrich and emu. Most taxonomic authorities recognize two extant species: the greater or American rhea ("Rhea americana") and the lesser or Darwin's rhea ("Rhea pennata"). The IUCN lists the puna rhea ("Rhea tarapacensis") as a separate species. The IUCN currently rates the greater and puna rheas as near-threatened in their native ranges, while Darwin's rhea is of least concern. In addition, a feral population of the greater rhea in Germany appears
Word square place names). However, 11-squares are possible if words from a number of languages are allowed ("Word Ways", August 2004 and May 2005). It is possible to estimate the degree of difficulty of constructing word squares. 5-squares can be constructed with as little as a 250-word vocabulary. Roughly, for each step upwards, one needs four times the number of words. For a 9-square, one needs over 60,000 9-letter words, which is practically all of those in single very large dictionaries. For large squares, the vocabulary prevents selecting more "desirable" words (i.e. words that are unhyphenated, in common use, without contrived inflections,