These are all plants that, from my point of view, are Yuccas. But for some minor quirk or oddity in their flowers, other anatomy or DNA, failed to make the cut into the Yucca family and have been lumped into families of their own. Hesperoyucca is the latest of these, with this local southern California yucca being uncerimonously scooted off into its own family not that long ago because of some chromosomal transgression. The root ‘Hespero' means western, which would describe the location of these plants in North America (all on the western half). It also means evening, which for most of these plants, doesn't really apply.
Hesperaloe means Western Aloe, which is an odd name as it looks to me very little like an aloe, but very much like a Yucca or perhaps an Agave (both its closer relatives, too). Hesperaloes are generally Mexican plants in the Agave subfamily (family of Asparagus), though several species can be found in Texas. What exactly separates Hesperaloes from Yuccas is a bit unclear, though some generalized differences have been mentioned in the literature: roots are fibrous and relatively shallow, more like an Agaves than a Yuccas; leaves are usually rolled or curled along their length and always with fibrous strands coming off the edges (like a few Yuccas- most have flattened leaves); they spread by rhizomes underground, like only some Yuccas and Agaves; and their floral anatomy is somewhat different than all Yuccas, though exactly how is not well explained. My personal, unscientific, casual observation is the flower panicles of Hesperaloes are more like some Agaves, being tall, long and sometimes arching with relatively small flowers (small for a Yucca at least) along much of their length (sort of a mix of an agave flower with a Yucca flower). All these plants are virtually stemless (or with short, underground stems) and have an upright growth similar to a patch of stiff, succulent grass (like many Yuccas and some Agaves). Unlike stemless yuccas, however, these tend not to have all the leaves shooting out of the ground from a single point, but from a broader area, giving them a bit more shrubby and less elegant look than most stemless Yuccas. None have succulent leaves like an Aloe nor flowers like an aloe, so I am still not clear on the Aloe-like appearance excuse for this name.
close ups of both the leaves and flowers of a Hesperaloe parviflora (photos by Xenomorf)
Yucca endlichiana, a true Yucca species, shown above is a similar looking plant with clumping rhizomous growth (left) and small but somewhat disimilar flowers (right) (left photo CactusJordi)
There are about 5-7 species of Hesperaloe, depending upon your source, but at least four of them are well known and grown. Hesperaloe parviflora is by far the best known in cultivation, being hardy, attractive, user friendly (not too dangerous), readily available and fairly easy to grow. Some of the others have been coming under scrutiny recently as sources of very durable paper, but neither are that ornamental.
Hesperaloe parviflora, or Red Yucca, False Yucca, Texas Red Yucca etc: This is a smaller species (about two feet tall) of clumping, stiff, slightly curved leaves that is a native of Texas as well as Mexico, but is pretty rare in Texas. It is, however, extremely common in the landscaping of many areas of the Southern US, even on the east coast, as it has a high tolerance for cold and seems to tolerate a somewhat humid climate well. It is very drought tolerant, too, and does great as a potted plant. It spreads by rhizomes and can slowly fill in an area with dense plant material. The best attribute are its showy pink panicles of flowers that bloom variable nearly half the year (from February to mid-summer) hence its name, Red Yucca. There are no thorns on this plant but the leaf tips are pointy so one could theoretically poke their eye out bending over to weed one of these plants. Interestingly there is a rarer pale-yellowing flowering form though it is still called Red Yucca. I have grown this plant both in the ground and in a pot and it is a reliable bloomer and incredibly care free. However, it is not the most ornamental plant in the yard (aside from its flowers). As a solitary plant, it is somewhat uninteresting, but makes a good landscape plant for mass plantings, particularly while flowering.
Hesperaloe parvifloras red flowers (left) and yellow flowers (right)
Hesperaloe parviflora panicle with immature, old and open flowers
Hesperaloe parviflora panicles with flowers (left) and later one, mostly seed pods/fruits (right)
Close up of leaf bases showing fibrous hairs and early flower (left); right shows yellow flowers (both photos Xenomorf)
Hesperaloe parvifloras in landscapes (California left- photo Kelli); and Arizona right (photo shindagger)
Hesperaloe funifera, or Giant Hesperaloe: As the name suggests, this is a much larger plant, upwards of four to six feet tall. It has very straight, stiff, curled bright green leaves with the typical fibrous threads on them, but tends to stay more solitary in appearance than Hesperaloe parviflora does. It is used as an accent landscaping plant, but also as a potential source, commercially, for paper production. It is extremely tolerant of high heat (excellent in Arizona) but not so of high humidity. Flowers are pale greenish white and occur in summer and fall. This plant looks even more like a Yucca than does Hesperaloe parviflora. Here is a link to its cultivation and growth as a paper source: http://www.ag.arizona.edu/~spmcl/Research/newcrops.htm
Hesperaloe funifera in Huntington Gardens, California (left); close up of leaf stalks showing fiber, of plant in Arizona (right photo Xenomorf)
Hesperaloe nocturna or Night Blooming Hesperaloe (here the term Hesper could be referring to its flowering time, evening): This is a relatively wispy plant looking more like a large, unruly clump of tall grass than a succulent-type plant from a distance. It is about five feet to six feet tall with thin, fibrous leaves that are curled on themselves longitudinally, and arch in various directions. Like the other Hesperaloes, it is very drought, cold and heat tolerant. It is grown as an accent plant, and potted plant in very dry, hot areas.
Hesperaloe nocturna (photo Xeno morph)
Hesperaloe campanulata or Bell Flower Hesperaloe: this is a smaller plant, similar in size to Hesperaloe parviflora, but more the shape of Hesperaloe funifera. It too is a native of south Texas and northern Mexico. This plant is a bit less ornamental in that it only flowers in summer and the flowers are pale pink to white. It is also significantly less cold tolerant (just down to 10F). Leaves are a pale green and curled on themselves longitudinally and include the typical fibrous hairs. This is another possible cultivated paper source.
Hesperaloe campanulata in Fullerton Arborteum, southern California
Hesperoyucca whipplei or Lord's Candle, Spanish Bayonet, Common Yucca etc.: this is one of maybe two species that only have recently been put back in this genus (thanks to DNA testing) but for many years (and still is by many societies) was included in the Yuccas. This is a monocarpic plant, native to the US Southwest and looks a LOT like a yucca, including the inflorescence. It is a striking and very common species near my area of southern California. Plants are generally pale blue-green, with very sharp, stiff leaves and a massive, almost agave-like inflorescence (at first) shooting up a deep red and turquoise panicle up to about fifteen feet high. Hundreds of seeds result so the subsequent death of the plant is often followed by a flourish of seedlings soon after. This is a very drought tolerant species but only cold tolerant down to about 10F. Hesperoyucca is used for soap or shampoo production.
Hesperaloe whipplei (left) Hesperaloe whipplei ssp. eremica (right)
Hesperoyucca in southern California
Hesperoyucca whipplei showing colorful new flower stalk
Hesperaloe whipplei flowering and showing floral details
Hesperoyucca flower spike with seed pods (left); Hesperaloe whipplei ssp. eremica in habitat (photo CactusJordi)
Yucca whipplei ssp. eremica flowering and flower details (right photo CactusJordi)
True Yuccas, Yucca peninsularis with early flower (left); and Yucca rostrata in flower (right) showing how similar some Yuccas are to Hesperoyucca whipplei