The letter x is used to represent the number of chromosomes in a single set:
haploid (one set; 1x)
diploid (two sets; 2x)
triploid (three sets; 3x), for example sterile saffron crocus, or seedless watermelons, also common in the phylum Tardigrada
tetraploid (four sets; 4x), for example Salmonidae fish, the cotton Gossypium hirsutum
pentaploid (five sets; 5x), for example Kenai Birch (Betula kenaica)
hexaploid (six sets; 6x), for example some species of wheat, kiwifruit
heptaploid or septaploid (seven sets; 7x)
octaploid or octoploid, (eight sets; 8x), for example Acipenser (genus of sturgeon fish), dahlias
decaploid (ten sets; 10x), for example certain strawberries
dodecaploid or duodecaploid (twelve sets; 12x), for example the plants Celosia argentea and Spartina anglica  or the amphibian Xenopus ruwenzoriensis. Classification
Autopolyploidy
Autopolyploids are polyploids with multiple chromosome sets derived from a single taxon. Two examples of natural autopolyploids are the piggyback plant, Tolmiea menzisii and the white sturgeon, Acipenser transmontanum. Most instances of autopolyploidy result from the fusion of unreduced (2n) gametes, which results in either triploid (n + 2n = 3n) or tetraploid (2n + 2n = 4n) offspring. Triploid offspring are typically sterile (as in the phenomenon of triploid block), but in some cases they may produce high proportions of unreduced gametes and thus aid the formation of tetraploids. This pathway to tetraploidy is referred to as the triploid bridge. Triploids may also persist through asexual reproduction. In fact, stable autotriploidy in plants is often associated with apomictic mating systems. In agricultural systems, autotriploidy can result in seedlessness, as in watermelons and bananas.
In some situations, polyploid crops are preferred because they are sterile. For example, many seedless fruit varieties are seedless as a result of polyploidy. Such crops are propagated using asexual techniques, such as grafting. Polyploidy in crop plants is most commonly induced by treating seeds with the chemical colchicine. Examples
Triploid crops: some apple varieties (such as Belle de Boskoop, Jonagold, Mutsu, Ribston Pippin), banana, citrus, ginger, watermelon, saffron crocus, white pulp of coconut
Tetraploid crops: very few apple varieties, durum or macaroni wheat, cotton, potato, canola/rapeseed, leek, tobacco, peanut, kinnow, Pelargonium
Hexaploid crops: chrysanthemum, bread wheat, triticale, oat, kiwifruit
Octaploid crops: strawberry, dahlia, pansies, sugar cane, oca (Oxalis tuberosa)
Dodecaploid crops: some sugar cane hybridsSome crops are found in a variety of ploidies: tulips and lilies are commonly found as both diploid and triploid; daylilies (Hemerocallis cultivars) are available as either diploid or tetraploid; apples and kinnow mandarins can be diploid, triploid, or tetraploid. Fungi
Besides plants and animals, the evolutionary history of various fungal species is dotted by past and recent whole-genome duplication events (see Albertin and Marullo 2012 for review). Several examples of polyploids are known:

autopolyploid: the aquatic fungi of genus Allomyces, some Saccharomyces cerevisiae strains used in bakery, etc. allopolyploid: the widespread Cyathus stercoreus, the allotetraploid lager yeast Saccharomyces pastorianus, the allotriploid wine spoilage yeast Dekkera bruxellensis, etc. paleopolyploid: the human pathogen Rhizopus oryzae, the genus Saccharomyces, etc.In addition, polyploidy is frequently associated with hybridization and reticulate evolution that appear to be highly prevalent in several fungal taxa.