Some of the brightest youngsters in the U.S. will square off on Thursday in the final round of the Scripps National Spelling Bee, a mind-boggling test of their mastery of the most obscure, complex and downright tricky words in the English language.

The one-day grand finale is the culmination of a quest that began with regional competitions that narrowed the field to 245 local winners, ages 8 to 15. They traveled with their families to a convention center outside Washington for "Bee Week."

Thursday's finalists survived three preliminary rounds in which their fellow contestants fell victim to such brain-teasers as "iridochoroiditis" (defined as an inflammation of the eye's iris), "keratophyre" (a compact porphyritic rock) or "nectocalyx" (a swimming bell of a siphonophore, which is a type of sea creature).

Challenged with some of the most difficult and least-used words that English has to offer, many of young competitors amazed spectators with their ability to conjure up the correct spellings with poise and precision.

Last year, Largo, Florida's Dev Shah, then 14, battled through 15 rounds and won the championship with his spelling of the word "psammophile" (a plant or animal that thrives in sandy areas).

The Scripps media group has sponsored the event since 1925, with three years off during World War Two and one more for the COVID pandemic in 2020.

This year's event offers a $50,000 prize to the winner or winners, according to the event's media guide.

If two or more spellers tie for first place, each will receive $50,000. In 2019, eight spellers tied for the title when organizers ran out of words considered challenging enough for the field.

Most competitors are from the United States, coming from all 50 states, the District of Columbia and the U.S. territories of Guam, Puerto Rico and the U.S. Virgin Islands. Canada, the Bahamas, Germany and Ghana are also represented this year.

(Reporting by Daniel Trotta; Editing by Frank McGurty and Cynthia Osterman)