Nick Jensen: TWO NEW SPECIES OF STREPTANTHUS: from the Tehachapi Mountains in Kern County
[rareplants.cnps/org] Background, Taxonomy, Ecology, Distribution, Status, Threats: Added to California Rare Plant Rank 1B.1 of the CNPS Inventory on 5 November 2020
Rare Plant Status Review: Streptanthus medeirosii
Proposed Addition to California Rare Plant Rank 1B.1, G1 / S1
Aaron E. Sims (CNPS), Jonathon Holguin (CNPS), and Katie Ferguson (CNDDB)
29 September 2020
Background and Taxonomy
Streptanthus medeirosii N.Jensen is a perennial herb in Brassicaceae known from Tejon Ranch
in the Tehachapi Mountains of southern Kern County, California. It was formally described as a
new species this year and is therefore not included in The Jepson Manual (Al-Shehbaz 1993),
Jepson eFlora (Al-Shehbaz 2012), or Flora of North America (Al-Shehbaz 2010). Streptanthus
juneae is another rare species described by Jensen (2020) that is known from the San Bernardino
Mountains in San Bernardino County, and is also being proposed for addition to California Rare
Plant Rank 1B in a separate status review.
Jensen (2020) described S. medeirosii and S. juneae based on phylogenetic, morphological,
geographical, and ecological evidence, utilizing a species concept consistent with Quieroz (2007)
and Freudenstein et al. (2016). Both species are included in the Southern Howellii Clade of
Streptanthus, a subset of the Howellii Alliance as first characterized by Cacho et al. in 2014. The
two previously described species of the Southern Howellii Alliance are S. bernardinus and S.
?Large wings at the apices of seeds distinguish Streptanthus medeirosii from all other perennial
Streptanthus? (Jensen 2020). The documented range of S. medeirosii does not directly overlap
with any other members of the Southern Howellii Clade, but one other perennial species, S.
cordatus, occurs nearby (Jensen 2020). Several diagnostic characters of S. medeirosii serve to
distinguish it from the potentially co-occurring and broadly distributed S. cordatus, including
strongly campanulate (bell shaped) calyces (vs. calyces that are not nearly as inflated
proximally), sepals that lack purple pigmentation (vs. sepals that are usually tinged pink to
purple apically or entirely pink to purple), and entire to sparsely dentate basal leaves (vs. basal
leaves with deeply dentate margins in S. cordatus) (Jensen 2020). See Jensen 2020 for additional
distinguishing characters between S. medeirosii and other members of the Southern Howellii
Clade, as well as a dichotomous key to the perennial Streptanthus and Caulanthus in California.
Streptanthus comes from Greek meaning ?twisted flower,? and the specific epithet, medeirosii, is
a Latinization of the name of the author?s friend and mentor, Joe Medeiros.
In southern Kern County?s cismontane mixed oak-fir forests, Streptanthus medeirosii occurs on
steep, rocky, east- or north-facing slopes of carbonate or granitic parent material (Jensen 2020),
between 1360?1880 meters in elevation (Google LLC 2020). It may also be found in rocky
outcrops along road cuts, preferring partial shade or full sun in sparsely vegetated areas (Jensen
2020). ?Streptanthus medeirosii begins flowering in early June. Flowering extends into early
September and fruit set occurs from July through September. Phenology, however, is variable
and governed by weather conditions.? (Jensen 2020). Streptanthus medeirosii was first collected
by Jensen in full flower on the last day of August in 2013. ?In contrast, plants had nearly finished
flowering by early August in 2017. Plants die back completely to a woody caudex each winter
Streptanthus medeirosii Element Code: ?
Sent to: SW, I. Al-Shehbaz, R. Raiche on 09/29/2020 Page 2 of 3
and are not detectable during dormancy; they resume vegetative growth in the late-spring.?
(Jensen 2020). Common associates include: Bromus diandrus, Chenopodium fremontii,
Eriogonum nudum var. pauciflorum, E. roseum, Erysimum capitatum, Hosackia crassifolia var.
crassifolia, Mentzelia albicaulis, Nicotiana attenuata, Penstemon grinnellii, Phacelia
ramosissima, and Sisymbrium orientale, Sambucus nigra subsp. caerulea (Jensen 2020).
Distribution and Abundance
Streptanthus medeirosii is known from three occurrences, all within Tejon Ranch of southern
Kern County (Jensen 2020). Record 1, based upon Jensen 524 and 2419, is the type location
situated farthest to the east of the known occurrences. It consists of only about 100 plants
growing over an area of approximately 0.2 hectares. The plants at this site are situated near a
regularly used dirt road and may be threatened by activities related to road maintenance. Record
2, based upon Jensen 4764, consists of approximately 50 plants spread over 0.1 hectares. Plants
at this site occur in a remote and roadless area and no known threats to this location are
characterized. Record 3 is known from a Laeger s.n. collection from 2017. Due to proximity to
the Tejon Mountain Village development area, the plants at this location were unavailable for
examination, and population numbers for the site are unknown.
Herbarium record Jensen 524 was mis-numbered and currently reflects a collection made of an
associated species, Sambucus nigra subsp. caerulea. This record will be corrected to reflect the
correct collection record at earliest convenience by the species? author (CCH 2020, Jensen pers.
comm 2020). Future fieldwork is likely to discover new occurrences of this species, as many
areas of suitable habitat have not yet been surveyed (Jensen 2020).
Status and Threats
Streptanthus medeirosii is threatened by development (record 3), and potentially threatened by
road maintenance (record 2) (Jensen 2020). Due to the recent nature of the discovery and
description of this species, considerations for Streptanthus medeirosii were not included in the
final Environmental Impact Report for the Tejon Mountain Village development area (Kern
County 2009). This taxon is highly vulnerable and should be considered for listing under the
California and Federal Endangered Species Acts.
Based on the available information, CNPS and CNDDB recommend adding Streptanthus
medeirosii to California Rare Plant Rank 1B.1 of the CNPS Inventory. If knowledge on the
distribution, threats, and rarity status of S. medeirosii changes in the future, we will re-evaluate
its status at that time. (contributed by Mary Ann Machi)