introduction to the Genus Yucca:
The Genus Yucca does only grow naturally in the new world,
it consists of about 50 species in the USA and about 30 species in Mexico
south to Guatemala (Yucca elephantipes). In the United States the
Genus Yucca range from the Atlantic seashore (Yucca
filamentosa) to the Pacific coast (Yucca
whipplei) and north into the southern part of Canada (Yucca
glauca ssp. albertana). Only in the Pacific north western
states and in the Atlantic north eastern states there are no Yucca
species (except for those in cultivation!). In the old world and other
places Yuccas has been introduced and has naturalized, but only vegetatively,
while Yuccas need a specific moth to be pollinated.
The only species that seems to produce seeds outside the new world is Yucca
aloifolia, which make viable seeds in the old world. I have reports
of fruits from: Spain (on several of the Spanish isle's), Italy, Switzerland
(Bodensee) and Hungary (Budapest botanical garden). During the last 15
years the number of available man
made hybrids has increased the palette of varieties suitable for cultivation
in the colder parts of the world, so now there are Yucca hybrids that can
be grown anywhere except of the extreme cold areas like Alaska.
Some species specially in the colder and northern parts of their
range, Yucca species tend to be small and trunk less, but in the warmer
and tropical areas, some species may become large branched trees up to
10 meter tall (Yucca brevifolia).
The leaves of Yucca can be rigid, pliable or even lax. The
leaf end can have a sharp or blunt spine or no spine at all. Many of the
species have marginal filaments which may be colored brown, yellow or white,
strait, curved, or curly. Others may have serrate leaves with many small
The flowers of Yuccas are quite alike, most are bell like and they
all have three sepals and three petals. The sepals and the petals are so
similar that they are referred to as tepals. The tepals vary in color from
greenish white to creamy white or clear white or even purple. (The flowers
can be used in salad!)
Yucca ovaries are superior with three chambers that contain many
ovules. The ovaries very much like those in the Liliaceae. About half the
species have woody dry capsules (dehiscent) similar to those of an Agave,
while the other half have fruits that are large and fleshy (indehiscent).
The seeds are black thin and winged in the dehiscent species and thick
(1-4 mm) in those that are indehiscent.
What really separates the genus Yucca from other flowering
plants are their special way to get pollinated. The pollination can only
be dome by a special moth in the Prodoxidae, that has been "programmed"
to do it! The female Yucca moth collects a ball of pollen and flies to
another Yucca flower where she squeeze the pollen down the pistil.
But before she leaves the flower, she lays an egg in the ovary, there the
larvae develop by eating some, but not all, of the maturing seeds.
The scientist used to think that there only were 3 different Yucca
moths; Tegeticula maculata which is specialized to pollinates Yucca
whipplei, Tegeticula paradoxa which is specialized to pollinates
brevifolia, and finally Tegeticula yuccasella which could
pollinate all the other species of Yucca. But the recent research
(Pellmyr 1999) has shown that there are many more species of Tegeticula
at least 16 different species, which all are specialized in pollinating
their "own" species of Yucca or Yucca species. It's actually
possible that there are even more species of Tegeticula, while the
research of the Yucca moths is still in progress. (Read
more about Yucca moths)
It is possible to pollinate Yucca flowers by hand
pollination, if you use two clones of Yucca plants, you will have a
better chance to succeed.
So far I have only specialized in growing the hardy species of Yucca,
therefore I have not written any pages about the Yucca
species south of the US/Mexican border. But when I run out of writing
about the US species I will start writing about the Species from Mexico
and south of there!