threonine: a colorless crystalline amino acid found in protein; occurs in the hydrolysates of certain proteins; an essential component of human nutrition
essential amino acid: an amino acid that is required by animals but that they cannot synthesize; must be supplied in the diet
sobralia: any of various showy orchids of the genus Sobralia having leafy stems and bright-colored solitary or racemose flowers similar to those of genus Cattleya