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| Arctostaphylos nipumu T.Abbo, M.A.Stickrod, A.Krohn, V.T.Parker, M.C.Vasey, W.Waycott & A.Litt., in Abbo, Stickrod, Krohn, Parker, Vasey, Waycott et Litt, 2025. |
Abstract
While investigating the potential for Arctostaphylos species to hybridize in the mixed populations of Point Sal and Burton Mesa in Santa Barbara County, California, we discovered that Arctostaphylos from the Nipomo Mesa (San Luis Obispo County), formerly considered a northern population of A. rudis, are genetically and morphologically distinct. We name this new taxon A. nipumu after the ytt (Northern Chumash language) word for the Nipomo Mesa region. For morphological and molecular analyses, we sampled 54 plants, focusing on A. purissima, A. rudis, and A. crustacea from multiple species and comparative single species populations. Parametric and nonparametric clustering analyses (STRUCTURE and PCA) of ddRADseq data show that Arctostaphylos from the Nipomo Mesa segregate from all other samples in the dataset. In mixed populations A. purissima and A. crustacea samples cluster with samples from other unmixed populations of the same species but A. rudis samples form two distinct clusters. One is composed of the mixed populations in Santa Barbara County, and the other consists of the Nipomo Mesa population. Additionally, the Santa Barbara County A. rudis samples are admixed in STRUCTURE analysis unlike the samples from the Nipomo Mesa. A principal component analysis of eight morphological characters shows that A. rudis individuals from Santa Barbara County tend to be phenotypically variable, occurring in a wide morphological cluster that overlaps with the tight clusters formed by A. purissima, A. crustacea, and Arctostaphylos from the Nipomo Mesa. Based on this evidence we describe the Nipomo Mesapopulation as a new species of Arctostaphylos. Given its limited and fragmented distribution we believe that A. nipumu is of critical conservation concern.
Key words: Arctostaphylos, conservation, ddRADseq, Ericaceae, fragmented population, hybridization, new species, reproductive isolation
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| Line drawing of Arctostaphylos nipumu. Top right (mature main trunk): bark shredding; base lacking burl. Top left (fruiting branch): twigs and petioles with moderately to very dense, short, nonglandular hairs; leaves generally lanceolate to ovate; fruit depressed. Bottom Left (nascent inflorescences): nascent inflorescences short/compressed; bracts overlapping, ± scale-like. Bottom center (flowering branch): inflorescences short, ± same length as nascent inflorescences; flowers urn-shaped. |
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| Diagnostic photographs of Arctostaphylos nipumu (Nipomo Mesa, San Luis Obispo County, CA) and A. rudis (Burton Mesa, Santa Barbara County, CA) A A. nipumu in situ, maritime chaparral habitat B depressed fruit of A. nipumu C nascent inflorescence, with leaf-like bracts proximally grading to scale-like bracts distally D A. nipumu, lacking a burl at the base of the stem F–H gray to reddish-gray, thinly shredding bark of A. nipumu E A. rudis with a pronounced burl at the base of the stem I–K pronouncedly red to reddish-gray, coarsely and variably shredding bark of A. rudis. |
Arctostaphylos nipumu T.Abbo, M.A.Stickrod, A.Krohn, V.T.Parker, M.C.Vasey, W.Waycott & A.Litt., sp. nov.
Description: Shrub up to 2, 3 (5) m ht. and < 10 m width; often layering, rooting when branches contact soil; burl 0 but with branchlets sprouting infrequently on stems; bark (red tinged) gray and shredding, from large stems up to new growth; twigs and petioles with moderately to very dense, short, nonglandular hairs; leaves isofacial (with stomata on both surfaces), green, shiny, generally lanceolate to ovate (elliptic to rounded with mucronate tip); blade 1.4–3.2 cm length, 0.9–1.9 cm width; petiole 0.4–0.8 cm; inflorescence a raceme or few-branched panicle (generally < 5-branched), nascent and mature inflorescences of similar length and thickness, 0.5 to 1.1 cm, and ca. 1 mm; bracts ± scale-like, often grading to ± leaf-like proximally, generally green, photosynthetic in summer; flowers 5-merous, urn-shaped, white to pinkish-white; fruit a multi-seeded drupe, generally reddish-orange, depressed axially; mesocarp mealy; endocarp generally rough, fused or separating into a variable number of nutlets.
Etymology: Based on discussions with the yak tityu tityu yak tiłhini (Northern Chumash Tribe), we selected the name Arctostaphylos nipumu because nipumu is the ytt (Northern Chumash language) word for the Nipomo Mesa region. The word nipumu is literally translated to English as “of the big house”, so we treat the epithet nipumu as a noun in apposition; ergo, Arctostaphylos nipumu is translated as “Arctostaphylos of the big house”. We recommend that A. nipumu be referred to by the common name nipumu manzanita or Nipomo Mesa manzanita; the latter regional name, Nipomo Mesa, is more well known in current usage, but the word Nipomo is an inferior Spanish transliteration of the word nipumu.
Tito Abbo, Morgan A. Stickrod, Alexander Krohn, V. Thomas Parker, Michael C. Vasey, William Waycott and Amy Litt. 2025. Investigating a hybrid mixed population leads to recognizing A New Species of Arctostaphylos (Ericaceae). PhytoKeys. 251: 119-142. DOI: doi.org/10.3897/phytokeys.251.139172
