Because of the technical aspect of this site
these articles were taken from a directory on Plant Yucca for accuracy purposes.
The background on these plants goes way back:
"Plant Yucca (Linnaeus 1757) (Indian: yuca = cassava)
There are at least 50 species of Plant Yucca within the Agavaceae, and numerous subspecies, varieties, forms, cultivars and hybrids of horticultural merit have been described. Several variegated cultivars are available, but may be less vigorous than non-variegates. Some common names such as "Palma", "Spanish Bayonet", "Spanish Dagger" etc. are used for several species, so are unhelpful identifiers".

"Plant Yucca occur exclusively in the Americas, distributed over a wide area from Canada into Central America and the Carribean with species adapted to dry deserts, grasslands and tropical rainforest's. Plant Yucca lacandonica is unusual in growing as an epiphyte on trees of the tropical rain forest of Southern Mexico and Guatemala. Wet-cold-hardy species suitable for UK-type climates are available with growth habits ranging from stemless rosettes to substantial trees. Species photographed in the RHS gardens, Wisley, UK have been growing outside for many years".

"All but one species (Y. whipplei) can flower many times (polycarpic) and produce side-shoots to compensate for loss of the apical growing point by its conversion into a flower bud.
Self pollination of Yucca flowers of many species is impossible, although a few are self-fertile. Most Yuccas are pollinated exclusively by small Yucca moths with the plant and moth totally dependent on each other. The female moth visits flowers collecting pollen into a ball which is deposited on the surface of the stigma after she has laid eggs deep in the flower ovary. The flower is sufficiently pollinated to ensure a multitude of seeds and provides food for the larvae, which eat only a few seeds".
Continued below: Plant Yucca

The real Plant Yucca Glauca;

The most common is " Plant Yucca glauca (Great Plains Yucca) flowering in the monocotyledon border of the RHS gardens, Wisley, UK in September 2003. It is widely distributed in North America and is hardy in the UK".
continued below: plant yucca

"This narrow-leaved species grows as a stemless clumping rosette, or may form a short 1ft stem with age, and is suitable for the smaller garden. Leaf margins carry white filaments".

The flowering Plant Yucca Baccata;

"Plant Yucca Baccata flowering at an altitude of around 1500 meters above sea level in the Coronado National Forest to the North of Phoenix, Az. The common name refers to the large edible fruit pods that are banana-like in shape. The pods, eaten raw, roasted or ground up and made into cakes, were an important source of food for Native Americans. The leaves were used to make mats and baskets".

"A Plant Yucca in this area will grow and flowered as delightful miniatures, suitable for the smallest garden. However, plant yuccas seen in New Mexico were much larger. This species is hardy and may even survive outside in a damp climate provided that its roots are very well drained. It has been seen growing outside for several years in the Royal Botanic Gardens.Plants in pots have grown on the author's patio through several winters. Plant
Yucca brevifolia (Joshua Tree) probably the most famous of all the Plant Yuccas, with a National Monument named after it and an indicator plant for the Mojave desert. Large specimens grow up to 10m tall. The inflorescence is a short panicle of greenish-white bells held close to the foliage.
Plant Yucca constricta (Buckley Yucca) from southern to central Texas.

Plants are stemless or with a very short stem carrying a clump of dis-organized rosettes of thin flat leaves with white filamentous margins. The inflorescence is up to 10 ft tall with small greenish-white flowers.