Hesperocallis undulata, Desert Lily, Fact Sheet
Don Rideout and Tom Chester
Fig. 1. Desert lily is one of the showiest desert species, with flowers similar in appearance to those of an Easter lily but with a somewhat-smaller size.
Click on the pictures for larger versions.
This page presents some basic facts about Hesperocallis undulata, in a brief format, to keep this page at a manageable size. A companion page elaborates on some of the information, and gives sources. This page was just begun on 29 March 2020, and so will be a work in progress for several years. It is modeled after the Lilium parryi, Lemon Lily, Fact Sheet, which might be interesting to some readers for comparison.
Table of Contents
Taxonomy and Phylogeny
Scientific Name origin: The genus name Hesperocallis is from the Greek hesperos, "west," and kallos, "beauty," and means "western beauty" (Charters 2009). The species was named and described by Asa Gray in the year 1867, published in Proc. Amer. Acad. of Nat. Sciences, Vol. vii, pp. 391, Boston, MA 1865-1868. Gray chose that name because he thought this species was related to Hemerocallis, the common day lily that is native to the Eastern Hemisphere (it is not related; see below). The name suggests that affinity, along with the far western, instead of eastern habitat (Gray 1867, quoted in Pires 2004). The specific epithet undulata means wavy-margined, referring to the usual wavy margins of the leaves (Charters 2009).
Common Name origin: No common name was given in the original 1867 paper describing the species, and we have not yet researched the first use of this name. In addition to "Desert lily", the early Spanish colonists called the bulbs "ajo", which is Spanish for "garlic", from the flavor of the bulb.
Discovery locality: The specimens mentioned by Gray were collected at "Desert Plains at Jessup Rapids, Arizona or New Mexico" by Newberry, and "Gravelly plains at Fort Mohave" by J.G. Cooper in 1860 or 1861, designed as a lectotype in 1994. Since desert lily does not grow in New Mexico, Jessup Rapids must have been in Arizona. The earliest collection was made by Fremont's Second expedition in April 24-25, 1844 from "sandy and gravelly uplands of the Mohave River"; see image of that collection.
The first vouchers from the Anza-Borrego Desert were from "Mt. Springs" by Sanford in 1892 and from Palm Creek on 18 April 1895 (presumably from Borrego Palm Creek; the voucher is georeferenced up the Canyon, but the voucher had to have been taken where it lives below the mouth of the Canyon).
Geographic Range: Sonoran and eastern Mojave Desert, southeast California, southwest Arizona, and the upper part of Baja and mainland Mexico, a range of 400 miles (650 km) north-south and 300 miles (500 km) east-west; see iNaturalist observation map with 2,440 observations as of 29 March 2020; SEINet voucher map for its entire range, and Borrego Desert map.
The Ajo mountains in southern Arizona are named for their scattered clumps of desert lily.
Elevation Range: Below sea level near the Salton Sea, to sea level in Baja California, to 2300 feet (700 m) in the eastern Mojave Desert, with outliers up to 2840 feet (866 m) in the eastern Mojave Desert.
Habitat: Dry sandy flats and washes; hills made of loose material forming gentle slopes; and even in poorly-consolidated sandstone or sandy conglomerate.
Population: TBD. This species is widespread at fairly low densities, but has small very dense patches in widely-scattered areas. The densest patch we know of consists of 163 plants in about a half acre in Don's yard in Borrego Springs. We fairly often see similarly-dense patches in smaller areas, but we've never seen anyplace where such very dense patches continue over areas larger than a half acre. The density is less than one per square mile on most alluvial slopes.
Desert Lily Sanctuary. As part of the California Desert Protection Act of 1994, Congress officially designated this 2000 acre site, located on the east side of State Highway 177 seven miles northeast of Desert Center. This designation was due to the effort of Tasker and Beula Edmiston. Ron's Log has a large number of photos from there.
Conservation Status and Threats to populations: No conservation status. Desert lily is a common desert species, so the species as a whole is not now under threat. Individual populations have been destroyed by agriculture, housing or commercial development, energy projects, and offroad vehicle use. In the future, climate change may become a threat to the species.
Major predators: Desert lilies are generally not subject to herbivory. We've never seen a bulb dug up by an animal, although there are reports that rodents, lagomorphs, and other small animals dig for the bulbs (Felger et al 2013); see a kangaroo rat unsuccessful attempt to dig up a bulb. Gophers are typically not present where desert lilies grow. Leaves and flower stalks are sometimes eaten by rabbits and hares, but the vast majority of plants we have observed do not have visible damage. Very unusually, in one survey, Don observed a number of flower / fruit stalks chewed off the plant with very little plant material consumed.
We have seen bulbs lying on the ground surface, presumably from erosion, that were untouched.
If the bulb is not damaged, the plant will survive to flower another year.
Potential insect threat. Rob Ferber grew desert lily bulbs in his geophyte garden in La Canada Flintridge, bulbs salvaged in 1991 from a construction site in 29 Palms. The desert lily bulbs, along with other bulbs he was growing, were destroyed in 1994 by the non-native Small Narcissus Bulb Fly.
At this time there is no indication that this fly is present in our desert. However, it is probably best if gardeners in Borrego Springs refrain from growing daffodils, and if nurseries and garden centers in Borrego Springs refrain from selling such bulbs. It would be terrible if this non-native insect became established in the desert and started destroying our beautiful desert lilies!
Native American Use: "The bulbs were baked or boiled, and also eaten fresh, probably in spring, but are rather slimy when fresh" (Felger et al 2013).
Cultivation: Desert lilies have resisted attempts at commercialization, due to difficulties in growing them from seed after the first year.
Demographics: To our knowledge, no one has ever done a long time-scale longitudinal study to truly know the demographics of the population. Don has observed the ~150 desert lilies on his Borrego Desert property for over ten years, and the population consists almost entirely of mature desert lilies (two or more leaves), with little observed recruitment. It is therefore likely that the population consists mostly of individuals more than ten years old. They are probably much older, but their actual age is unknown.
Life Form: Geophyte, from an underground tunicate bulb, a few inches below the surface for seedling plants to over 12 inches below the surface for mature plants. Some reports are of bulbs 24 inches deep. The bulb consists of concentric scales with a paper-like covering (the tunic), like an onion bulb. See a bulb split in half. Native Americans used the bulb for food.
Only 8% of California geophytes are typical desert taxa (Rundel 1996).
Bulbs must be able to move down in soil. Don found that a bulb originally planted in the middle-depth of a pot without a bottom had migrated to the below the bottom of the pot one year later. The obvious mechanism would be a contractile root, found in a close relative, Chlorogalum, and in true lilies. On 24 April 2021, Don found a contractile root on one of his potted desert lily bulbs; see photo!
The downward bulb movement is assisted by the fleshy roots under the bulb, which push out all the soil to the side as they grow. When those roots wither, the bulb could eventually move into the opened space. This is known to be important in the function of many contractile roots (Putz 2002, in Waisel et al 2002).
It is not known whether the bulbs can produce bulblets attached to a mother bulb. In the field, we often encounter two plants growing a bulb's width apart, which might be due to one bulb splitting, or might simply be due to two plants that started from seed side by side. We've never encountered a group of four or more plants growing a bulb's width apart that might be expected if a bulb produced multiple bulblets like Broadiaea and Dichelostemma do with their cormlets.
Bulb weight correlates strongly with the number of leaves it produces, from 6.3 g for a bulb producing a single leaf, 12 to 28 g for bulbs producing two leaves, 30 g for bulbs producing three leaves, to 39 g for bulbs producing four leaves. Weight was measured immediately after excavating the bulbs from Don's Borrego Springs yard.
Lifetime: unknown. Certainly at least decades, and possible centuries. It is not known how long bulbs can survive in the ground without water, but Don has observed plants in his Borrego Springs yard that have survived through three consecutive severe drought years, similar to what creosote can survive.
Seed Germination: Seeds germinate readily, but surviving their first summer and first winter is difficult. Don placed fresh seeds on potting soil in Summer 2017, watered them, and 14 of 15 seeds germinated within a week.
In Fall 2017, Don placed 150 seeds in containers in his Borrego Springs yard to observe what happened naturally. The 2017-2018 rainfall season was very dry, and no seed germinated. Those same one year old seeds germinated in the 2018-2019 rainfall season.
Time from Seed Germination to Flowering Plant: Our guess is possibly three to five years, but we don't know for sure. Don has been growing plants from seed for several years now, so he should eventually find out.
Stem: Seedling plants have no stem, just a single leaf. (add subsequent development). Mature bulbs, when they flower, almost always produce a single stem, but we know of one bulb that produced two flower stalks from the center of the bulb; another that produced three stalks from the center of the two bulbs; and one that produced three stalks, two from the bulb center and one from the side of the bulb that is probably about to be a bulblet. Most of the time when two flowers stalks are seen immediately next to each other in the ground, they come from separate bulbs, which can generally be seen by noting that there are two sets of leaves, one set associated with each bulb.
Stem height of blooming plants usually ranges from one to three feet above ground, plus one to two feet below ground. The stem height quoted in the floras includes the below-ground part.
Stems are usually unbranched, but robust plants can have many branches, each of which bears many flowers.
Leaves: The basal leaves are usually blue-green in color, long and strap-like, folded along the midline, usually (but not always) with wavy margins. Plants growing in hard soils often have much shorter lanceolate leaves. The leaves have parallel veins typical of monocots. The strap-like basal leaves are typically 8 to 20 inches (20 to 50 cm) long, and 1.5 to 2.5 inches (4 to 6 cm ) wide. The leaves on the flowering stem are technically called bracts, and grade from long strap-shaped leaves near the base to short stubby bracts under each flower.
The number of leaves varies from a single leaf in young plants, to possibly as many as eight and nine in very robust plants. It is often difficult to know for sure, without digging up the bulb, whether the leaves are coming from a single bulb or two bulbs; for example, this group of 11 leaves and two flower stalks is almost surely coming from two separate plants since the leaves come from two different centers.
Most plants in Don's Borrego Springs yard have two to four leaves, and most plants in a surveyed area in Carrizo Creek have two to five leaves. Compared to Don's yard, in other areas in the Borrego Desert there are more plants with six or more leaves, and fewer plants with one or two leaves.
Relationship between number of leaves and ability to flower. In Don's Borrego Springs yard, in a good year, all plants with three or more leaves produced a flower stalk, and just two out of 54 plants with two leaves produced a flower stalk. The total leaf area tracked closely with the number of leaves, since the leaves are all roughly the same size. The median leaf area for 48 plants was 404 cm2, corresponding to plants with three leaves.
In an area surveyed in Carrizo Creek, most, but not all, plants with more than four leaves produced a flower stalk, and just three out of 11 plants with three leaves produced a flower stalk.
Progression of Flowers and Fruit: Buds emerge from the top of the stem erect, and become ascending as they enlarge and the pedicels elongate. Flowers are ascending to spreading (horizontal) at bloom. The fruit becomes erect.
Variation in the number of flowering plants with year / Rainfall needed to produce growth: Desert lilies do not appear above ground in dry years, and evidence from Don's yard is that the plants can survive multiple drought years in a row without producing any above-ground growth. Some years the plants may produce only vegetative growth above-ground. Wet years cause essentially every mature plant to bloom. A cumulative rainfall of 1.5 to 3 inches in fall / winter is needed to penetrate the ground to the one to two foot depth of the roots, assuming a penetration factor of nine in sandy soil.
Flowering time: Desert lilies have been observed to be in bloom in at least one year in the months of December to May. However, the actual bloom duration in a given year can be as short as two weeks in drier years. To have a long blooming period in a given year requires some areas to receive monsoonal rain to produce an early bloom, with other areas receiving only winter rain to produce a later bloom.
Late rains can sometimes stimulate a plant to produce new flowers, even though it was already in fruit. On 28 March 2020 in the Carrizo Creek area, many were in fruit; two were both in full fruit AND blooms; a number were in full bloom; and one was just sending up its flower stalk, at least a week from blooming. The ones in full fruit and blooms looked they had stopped blooming due to lack of water, but then recent rains rejuvenated them. On 12 March 2016, a plant was observed to have several fruit in the lower part of its flowering stalk; seven buds / flowers / recent flowers well above the fruit; a stretch of seven aborted buds above the flowers; and six buds at the top of the stalk that were still developing.
An individual plant with a large number of flowers was observed by Bill Sullivan to go from its first blooms on 25 February 2016 to its last blooms on 4 March 2016, a period of just eight days.
Anatomy of a Flower: See labeled photograph. Each flower is similar in appearance to that of the Easter lily, each with six white "petals", but is somewhat smaller in size, typically 1.75 to 2.25 inches (4.5 to 6 cm) long and 2.5 to 3 inches (6 to 8 cm) wide. Monocots often have three sepals which look like petals, in which case they are called "tepals". If you look closely, you'll see the two sets of three tepals, an inner set and an outer set.
The tepals are white, with a wide silver-green to purplish midstripe on the outside (Easter lilies don't have that midstripe; they are pure white on the outside except sometimes with a faint green narrow midvein). There are six stamens and a slender style that is somewhat three-lobed.
Number of Flowers: Most commonly, an individual bulb produces a single flower stalk, which typically has four to 18 flowers over its lifetime, with two to three flowers open at a given time. The maximum number of flowers observed was ~140; look especially at the shadows of the inflorescence here and here.
Time Flowers Open and Close: Buds open in late afternoon and produce a flower in full bloom then. The flowers begin closing the next day, and are probably finished blooming the day after that; see Fig. 2.
12 March 2016 15:37
12 March 2016 17:50
13 March 2016 11:44
13 March 2016 17:53
Fig. 2. The progression of the same bud / flower over 26.25 hours. Click on the pix to see photographs of the entire plant at iNat, with the buds / flowers / finished flowers numbered. The bud / flower shown in this figure is #1. Bud / flower #2 opened at the same time as #1.
Note that the anthers are bright yellow when the flower opens, but look significantly withered by noon the next day. Although the same flower was not photographed on the second day after opening, it probably looks like this finished flower on the same stalk that was observed the first time it was closed (#3 in the pix linked from the pix in Fig. 2).
Individual Flower Lifetime: The tepals are probably open for just 24 to 36 hours, and the flower may be fertile only the first night it is open. Most probably, 48 hours after opening the tepals have withered to a transparent, papery texture covering the ovary. We can only say "probably" for those numbers since we've never followed an individual flower for more than two days, so we can't rule out the flower staying open longer. But it seems unlikely that it does.
Fragrance of flowers: Fragrant, especially at night, to attract its night-time pollinator.
Pollinator: White-lined sphinx moths, Hyles lineata, possibly also other insects and hummingbirds. Sphinx moths, including Hyles lineata, also pollinate lemon lilies high up in the mountains! Grant (1983) listed just 105 species in 16 families that have hawkmoth flowers (ones with a nectar tube of 2 to 7 cm, in some cases up to 9 to 20 cm) in North America north of Mexico.
Fruit. The fruit is an erect pudgy short 0.5 to 0.6 inch (12 to 16 mm) long capsule with three chambers, splitting at the top to release its seeds.
Seeds. The seeds are black, roughly flat, 0.2 inch (5 mm) in diameter; see about 100 seeds on a dinner plate.
Number of Seeds per Fruit: 70 to 100. In 2017, three fruit in Don's Borrego Springs yard held 282 intact seeds, an average of 94 per fruit.
Number of Flowers Producing Fruit: In contrast to lemon lilies, where essentially every flower produces fruit, desert lilies typically only produce one to three fruits per stalk, 15 to 50% of their total number of flowers. The maximum number of fruit we know of was 11, by far the record, with the runner-up having nine fruit.
Of the 163 plants in Don's Borrego Springs yard in 2017, 82 plants flowered; 24 plants produced fruit; 13 plants produced one fruit, 11 produced more than one fruit, with a total of 40 fruit produced from all 163 plants. The estimated total number of seeds was 3,760.
It is not known why so few desert lily flowers produce fruit, but it may be due to water availability and/or the shorter time its flowers are fertile:
- Lemon lilies are not limited by water; desert lilies are; see the "Flowering time" comments above about the effect of late rains. Don has also noted that fruit at the end of the season tend to be smaller.
- A desert lily flower is only fertile for one night. If the pollinators are busy elsewhere that night, or not present due to wind, cold, or rain, it won't get pollinated. In contrast, lemon lily flowers are probably fertile for at least several nights.
Predation of Fruit: Most fruit develops untouched. A small number of fruit are half-eaten at their tip by some unknown predator, perhaps a bighorn sheep, and insects.
Dispersal of Seeds: It is likely that wind can disperse the light flat seeds, but probably not for great distances most of the time, since the seed capsules are usually very close to the ground. However, some capsules at the tip of the flower stalk might be able to disperse seeds over larger distances.
Viability of seeds: Unknown.
Taxonomy and Phylogeny
Classification. Desert lily, like most geophytes, are monocots. Desert lily is the only species in its genus, with no subspecies or varieties. Its taxonomy is unusual, since the name has remained the same ever since it was proposed in 1867, and no one has ever proposed any subspecies or varieties. This is undoubtedly due to its relative uniformity across its range, and the lack of any close relatives.
Due to the lack of any close relatives, botanists have argued for a century about what plant family it is in; see Family Placement. Molecular data shows that desert lily is part of the Agavaceae family (Pires et al 2004), and thus is not a "true lily" in the lily family.
Origin of Hesperocallis species: Not known. It is a member of the subfamily Agavoideae, which has about 640 species in ~23 genera and is widespread in tropical, subtropical, and warm temperate regions.
Sister Genera Sharing a Common Ancestor: Possibly Camassia and Chlorogalum.
Evolutionary Group: Desert lily is part of the "Agavoideae bimodal karyotype (ABK) clade", which have a set of large chromosomes and a set of small chromosomes. Most of the clade have 25 small and 5 large, or some multiple of that, whereas five genera in the clade (Camassia, Chlorogalum, Hastingsia, Schoenolirion, and Hesperocallis) have diverged from the others, with Hesperocallis possibly most closely related to the first two genera, as first proposed in 1948 (McKain et al 2012). Desert lily has 18 small; two medium; and four large chromosomes, so something interesting happened in its evolution from the 25 small and 5 large crowd.
Closest relatives: Not clear, since Hesperocallis usually turns up as a sister species to everyone else in different analyses, but possibly Chlorogalum. Chlorogalum is a geophyte with many of the same characteristics as desert lily, with a similar edible bulb; basal undulate leaves that are quite similar to desert lily; and similar persistent dried corollas.
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Updated 27 June 2021.