Fun with Munz’s Mariposa Lily (Calochortus palmeri var. munzii)

A Rare Plant

By Fred Roberts, Chairperson Rare Plants Committee

Following up on a piece I wrote last summer (Rare Plant Hunting in a Dry Year, CNPS San Diego Chapter Newsletter, August 2018), I wanted to report on one of the species mentioned, Munz’s mariposa lily (Calochortus palmeri var. munzii, right), a California Rare Plant Rank 1B.2 plant. As I related last summer, in early June 2018, Jenny Moore, at the time the staff botanist for the Cleveland National Forest, had found an interesting mariposa lily near Buckman Springs south of I-8. It certainly looked a good deal like splendid mariposa lily (Calochortus splendens) but something was off and she wondered if it represented a hybrid 8 (you can see Jenny’s original plant on iNaturalist, it is the only record oniNaturalist south of I-8).

I’ve been looking for this species in San Diego County for about seven years so when she sent me her image that clearly showed yellow hairs at the base of the petal, not white, I knew exactly what it was (interestingly, there was a parallel conversation in the comments under her iNaturalist post where the commenters had come to the same conclusion). Jenny took me to the site in the first week of July 2018. Unfortunately, the plants were not in the best condition and there were too few plants present to collect a voucher specimen. We vowed to follow-up on this rare plant in 2019.

I’ve been quite interested in this plant as it occurs in San Diego County. When it first was added to the San Diego plant lists, it was known from about a half dozen sites, and with the exception of two collections from the Chihuahua Valley and near Warner Springs from 2010 and 2009 respectively, all the collections were old. It was almost absent from the San Diego Plant Atlas. Clearly it was not an abundant plant.

Sadly, from our perspective (but not necessarily from Jenny’sperspective), Jenny left the Cleveland National Forest office and moved to the northwest where the Forest Service actually manages forests. Despite a busy spring, I managed not to forget that I still intended to get a collection of Munz’s mariposa lily at this site.

On a hot day at the end of June, I drove out to the site, using a key acquired from the Forest Service (largely for my research on the 22,000-acre Holy Fire in the Santa Ana Mtns) to get through the locked gate.

Already, it was pretty warm by the time I had reached the gate at 10:00. Pippin, our Corgi, thought that the only place that needed to be examined was the cool underside of the 4Runner (he is such a city boy). I slowly drove the roads, looking for openings in the redshank (Adenostoma sparsifolium), especially those dominated by Great Basin sagebrush (Artemisia tridentata). To my delight, I found the mariposa lily, not just at the site where Jenny had taken me to last year, but another site as well. There were about 75 plants a the first site and over 200 at the destination site. In addition to recording numbers and mapping the two sites, I was able to get a proper voucher for both sites.

As it turns out, you can find one other 2019 observation for this plant in San Diego County on Calflora, where it is reported from the Pacific Crest Trail near Warner Springs. Ironically, I have looked for it in that general area for the most of the last decade without luck. Except this year. It looks like 2019 would have been a good year to canvas the back country for this plant.

Fun with Munz’s Mariposa Lily 2.jpg

At a glance, Munz’s mariposa lily (left) really does look a lot like splendid mariposa lily. For decades, San Diego County plants masqueraded under this name. Munz’s mariposa lily is separated from splendid mariposa lily by the presence of yellow clavate (club-shaped) and white, or very pale lavender anthers vs. dark, often blue or purple anthers. The yellow hair character is shared with or shy mariposa lily (Calochortus invenustus), for which it could also be mistaken. However, shy mariposa lily will have a green stripe on the back of the petal and is often white or purple but seldom shares the pinkish-lavender color of Munz’s or splendid mariposa lily. In San Diego County, shy mariposa lily is often seen in somewhat more mesic habitats,
this name as along the Sunrise Highway in the Laguna Mtns. while Munz’s mariposa would be farther east.

Fun with Munz’s Mariposa Lily 3.jpg

Palmer’s mariposa lily (C. p. var. palmeri) shares most characteristics, except that the inflorescence is often with 1-6 stems and alternate bracts while Munz’s mariposa typically has paired inflorescence branches, has opposite bracts, and does not forms bulblets. The flowers are more typically white (rarely pink lavender), often smaller, and more open, sometimes almost laid out flat, the bracts are alternate in arrangement, and forms bulblets at the base of the stems.Most significantly, Palmer’s mariposa lily is found along streams and in wet meadows in the higher mountains from San Luis Obispo Co. to the San Bernardino Mtns. Munz’s mariposa lily is found in dry habitats of the Peninsular Ranges.

I’ve told this story often but think it worth telling again. Until recently, Munz’s mariposa lily was thought to be endemic to the San Jacinto Mountains of Riverside County. Jon Rebman found a mariposa lily at the top of the Sierra la Libertad in 2009. The nearest mariposa lily records were about 200 km to the north in the Sierra San Pedro Mártir Mountains. After some investigation, it appeared that theclosest fit to this lily was Palmer’s mariposa lily, or morespecifically, the variety named after Phillip Munz. An examination of herbarium specimens showed that the taxon was more widespread in northwestern Baja California where specimens had been masquerading as splendid mariposa lily. Could this be true for San Diego County as well? This was much closer to the traditional range in Riverside County. In 2011, Jon reviewed the San Diego County collections of splendid mariposa lily and shy mariposa lily and found that some of these plants, mostly from east county, sometimes on the desert fringes, where indeed Munz’s mariposa lily. Thus, the range of this rare plant actually extends from the San Jacinto Mountains at the north end of the Peninsular Ranges south to the southern Sierra San Pedro Mártir of Baja California, with an isolated site in the Sierra la Libertad, quite an upgrade from San Jacinto Mountain endemic.