The various species of Boechera are extremely difficult to tell apart. The Flora of North America states,

The taxonomic complexity of Arabis, in the broad sense, is legendary (R. C. Rollins 1941, 1993; G. A. Mulligan 1996). When the genus is split, most of the problematic taxa come to reside in Boechera. A rare confluence of hybridization, apomixis, and polyploidy makes Boechera one of the most difficult genera in the North American flora. 

    The authors of Intermountain Flora indicate, "The morphological similarities [of Boechera] appear to be due to convergent evolution, a curse with which the Brassicaceae burdens us."      

    If you compare Boechera keys in the various floras that cover the Four Corners region, you will see that there is not even agreement on which species exist in our area.  

     I used a number of keys to identify the species shown on this page, but even then I misidentified the Boechera species that I commonly see in the Four Corners region. Superb botanist, Patrick Alexander, alerted me to my misidentifications and indicated that a number of Boechera shown in my photographs are probably a new species "provisionally called Boechera 'quadrangulensis' (included in Boechera duchesnensis in the Flora of North America treatment)".

    Patrick further indicated that the Boechera key in the Flora of the Four Corners Region is the best available. Also see the Flora of North America key co-authored by Mike Windham, the author of the Four Corners flora Boechera key.

     I entered the above information from approximately 2005 to 2015, but in 2022 Windham et al. published results showing even more complexity in the Boechera genus. The "Introduction" to "An Overview of New Mexican Boechera" states,

Over its relatively short evolutionary history, the mustard genus Boechera has experienced a phenomenal amount of evolutionary diversification (Rushworth et al. 2011). Although the most recent broad-scale taxonomic treatment for the genus (Al-Shehebaz & Windham 2010) recognized just 111 taxa in North America, ongoing genus-wide microsatellite analyses paint a very different picture (Li et al. 2017). These studies reveal that in addition to +/- 83 genetically recognizable sexual diploid taxa, the genus includes 400+ polyploid and/or apomictic hybrids representing diverse combinations of at least 64 of the known sexual entities. Clearly, significant adjustments to the current taxonomy will be needed if we hope to produce a classification usable by a diversity of stakeholders. This effort will require both significant expansion of existing species boundaries as well as the segregation and naming of new species that cannot otherwise be accommodated in the classification.

     For two centuries "Arabis", a name given by Linnaeus in 1753 to Old World species, was the accepted genus name for all the similar New World plants.  Genetic research by Löve and Löve led them to believe that the Old World genus and the New World genus were not the same and in 1978 they created the Boechera genus.  In 1982 William Weber furthered their work and reassigned almost all New World Arabis species to the Boechera genus; most botanists now accept that classification.

     However, the eminent botanist, Stanley Welsh (A Utah Flora, 5th edition), retains Arabis as opposed to what he feels is the "narrower view" removing North American species to Boechera. Welsh points out that,

"Recent recognition of "Boecher" in Old World species negates the supposed geographical distinction [between Boechera and Arabis].... One should not have to carry around with them a laboratory or a computer to make determinations of "molecular or cladistic phylogeny " prior to placement of genera, and at the same time toss away morphological considerations".

    Tyge Boecher was a 20th century Danish botanist who studied the flora of Greenland.  Boechera is often pronounced "Boo-ker-uh" or Beck-er-uh".  (More biographical information about Boecher). 

Click to see Boechera afflicted with yellow Puccinia rust.

Semi-desert, foothills. Woodlands, shrublands, openings. Spring.
Above: Lower Cross Canyon, Utah, April 10, 2016.
Left: Grandstaff Canyon, April 1, 2004 and
Behind the Rocks Wilderness Study Area, Utah, April 14, 2009.

This slender, dainty, and lovely (thus the Latin, "formosa", meaning "beautiful" or "graceful") member of the Mustard Family grows in open, sunny, semi-desert areas of the Four Corners.  The plant is easily passed by because it is so slender and its flowers are so pale, varying from nearly white to pink to lavender-purple.

Though the flowers are small, they are most often larger than the flowers of other Boechera in our area: petals are usually greater than 10 millimeters whereas others are smaller than 10 millimeters. In addition, B. formosa is set off from other local Boechera by having pubescent fruits and densely pubescent upper cauline leaves that lack auricles (an ear-shaped projection at the base of the leaf). Other Boechera species have glabrous fruits and glabrous to sparsely pubescent upper cauline leaves, or, if the upper leaves are densely pubescent, then whey will have "well-developed auricles". (Descriptive material from The Flora of the Four Corners Region.) 

M. E. Jones named this plant Arabis pulchra in 1887 from a specimen he collected in Nevada in 1882. Edward Greene named the plant Arabis formosa from a collection that Charles Baker made in Aztec, New Mexico in 1899. The plants in the Four Corners region were known for years as Arabis pulchra. In 1982 William Weber revised the Arabis genus and moved most species to the Boechera genus, a move which most botanists accept. In the early 2000s Windham and Al-Shehbaz determined that Boechera pulchra is a species just of California and that Boechera formosa is "confined to sandy or rocky habitats in the Four Corners states" (although Kartesz's range map below shows it with a wider area of distribution).

"Formosa" means "beautiful".

Semi-desert, foothills. Woodlands, shrublands, openings. Spring.
Lower Cross Canyon, Utah, April 10, 2016 and Mc Elmo Canyon, April 25, 2009.

Boechera formosa is quite hairy and, in fact, it is quickly separated from other Boecheras by the hairiness of its fruits (its "siliques"). The arrow in the top photograph at left points to a newly developing silique that is clothed in a myriad of minute, branched hairs that impart a fuzzy glow. The silique is surrounded by the green filaments topped by yellow/brown anthers and these are all surrounded by the calyx.

Siliques become more and more pendant as they elongate.

Semi-desert, foothills. Woodlands, shrublands, openings. Spring.
Lower Cross Canyon, Utah, April 10, 2016 and April 17, 2020.

In the photograph below, the long, woody projection below the basal rosette of leaves is the caudex, the herbaceous stem's woody base.

The loose basal array of leaves and the stems are clothed in a myriad of branched hairs that impart a white glow. Branching hairs are characteristic of this genus.

Some species of Boechera can have tight clusters of basal leaves and no caudex.

Semi-desert, foothills. Woodlands, shrublands, openings. Spring.
Lower Cross Canyon, Utah, April 10, 2016.

Boechera quadrangulensis. Synonyms: Boechera duchesnensis, Boechera pulchra var. duchesnensis.  (Desert Rockcress)
Brassicaceae (Mustard Family)

Semi-deserts. Shrublands, openings, woodlands. Spring.
Canyons of the Ancients National Monument, March  10, 2016.

This delicate Boechera grows to be about as tall as B. formosa (see above), but it has much smaller flowers and it differs even more dramatically from B. formosa in that its seed pods (siliques) are glabrous to sparsely hairy near their tips versus the densely hairy seed pods of B. formosa. Also, as shown below, B. quadrangulensis has leaves with ear-like appendages; B. formosa does not.

Flower color in all the Boechera shown on this page ranges through blue/purples and pinks to occasional whites. The Boechera plants also share similar Sagebrush and Pinyon/Juniper woodlands habitats. 

The siliques (seed pods) of this Boechera are long, narrow, and project outward or arch downward from the stem.

The Flora of North America notes that "Morphological and isozyme analyses indicate that Boechera duchesnensis is an apomictic species that arose through hybridization between B. formosa and B. pallidifolia".

"An Overview of New Mexican Boechera", further research published by Windham and Pryor in the July, 2022 "Journal of the Botanical Research Institute of Texas" indicated that the species in the Four Corners area was not the same as Boechera duchesnensis and should be regarded as a new species, Boechera quadrangulensis:

"Specimens previously attributed to B. duchesnensis from the Four Corners region are stable apomictic triploids containing genomes from B. pulchra ssp. pallens, B. crandallii ssp. kelseyana, and B. perennans ssp. perennans. Analyses conducted using the Boechera Microsatellite Website (Li et al. 2017) indicate that this trigenomic triploid arose in the Four Corners region through hybridization between B. pulchra ssp. pallens (a sexual diploid) and an apomictic diploid lineage belonging to B. gracilent a s.l. [sensu lato", i.e., "in a wide sense"(Windham et al. upubl.). Here we name this newly documented hybrid as: Boechera quadrangulensis."

The specific epithet refers to the exclusive location of this species: the Four Corners area "quadran" "ensis").

Boechera quadrangulensis. Synonyms: Boechera duchesnensis, Boechera pulchra var. duchesnensis.  (Desert Rockcress)
Brassicaceae (Mustard Family)

Semi-deserts. Shrublands, openings, woodlands. Spring.
Canyons of the Ancients National Monument, March  10, 2016 and April 22, 2016.

Flower sepals are quite hairy. Flower buds are erect and flowers gradually decline as they mature.

Fruiting pedicels are horizontal. The siliques with six or seven dozen seeds are about 1 1/2 mm wide, 35 mm long, glabrous, and curved downward.

Boechera quadrangulensis. Synonyms: Boechera duchesnensis, Boechera pulchra var. duchesnensis.  (Desert Rockcress)
Brassicaceae (Mustard Family)

Semi-deserts. Shrublands, openings, woodlands. Spring.
Canyons of the Ancients National Monument, March  10, 2016.

The white cast to the stems and leaves is from hairs which are especially prominent on the basal leaves. When you find these plants, take a look at the hairs with a hand lens. You will be intrigued. The hairs are silvery and in a star-burst pattern with 2-7 rays.

Stem leaves clasp the stem

and project downward (like ear lobes) on either side of the leaf base.

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Range map for Boechera formosa