A genus of herbaceous perennials native to Mexico and Central America. They have tuberous roots that can be stored over winter for those in harsher climates. There are 42 species and probably tens of thousands of hybrids. This is because the plants have 8 sets of chromosomes, where 2 is normal. They also are prone to mutations. That lends them to having a great amount of variety in their progeny.
There are multiple groupings of flowers:
Group 1: Single. Flower has a central disc with a single outer ring of florets (which may overlap) encircling it, and which may be rounded or pointed.
Group 2: Anemone. The center of the flower consists of dense elongated tubular florets, longer than the disc florets of Single dahlias, while the outer parts have one or more rings of flatter ray florets. Disc absent.
Group 3: Collerette. Large flat florets forming a single outer ring around a central disc and which may overlap a smaller circle of florets closer to the center, which have the appearance of a collar.
Group 4: Waterlily. Double blooms, broad sparse curved, slightly curved or flat florets and very shallow in depth compared with other dahlias. Depth less than half the diameter of the bloom.
Group 5: Decorative. Double blooms, ray florets broad, flat, involute no more than 75% of the longitudinal axis, slightly twisted and usually bluntly pointed. No visible central disc.
Group 6: Ball. Double blooms that are ball shaped or slightly flattened. Ray florets blunt or rounded at the tips, margins arranged spirally, involute for at least seventy five percent of the length of the florets. Larger than Pompons.
Group 7: Pompon. Double spherical miniature flowers made up entirely from florets that are curved inwards (involute) for their entire length (longitudinal axis), resembling a pompon.
Group 8: Cactus. Double blooms, ray florets pointed, with majority rolled over more than 50% of their longitudinal axis, and straight or incurved. Narrower than Semi cactus.
Group 9: Semi cactus. Double blooms, very pointed ray florets, revolute for greater than 25% and less than 50% of their longitudinal axis. Broad at the base and straight or incurved, almost spiky in appearance.
Group 10: Miscellaneous. Anything not included in the other groups.
Group 11: Fimbriated. Ray florets evenly split or notched into two or more divisions, uniformly throughout the bloom, creating a fringed effect. The petals may be flat, involute, revolute, straight, incurving or twisted.
Group 12: Single Orchid (Star). single outer ring of florets surrounds a central disc. The ray florets are either involute or revolute.
Group 13: Double Orchid. Double blooms with triangular centers. The ray florets are narrowly lanceolate and are either involute or revolute. The central disc is absent.
Group 14: Peony. Large flowers with three or four rows of rays that are flattened and expanded and arranged irregularly. The rays surround a golden disc similar to that of Single dahlias.
Books to Consider
Pronunciation: DAHL-ya or DAY-lee-ah
Name Derivation: Named for Dr. Andreas (Anders) Dahl, 18th century Swedish botanist and student of Linnaeus
Dahlia is in the family Asteraceae.