|A new Ambrosia (Asteraceae) from the Baja California Peninsula, México
José Luis León de la Luz1 and Jon P. Rebman2
1Herbario HCIB, Centro de Investigaciones Biológicas del Noroeste, Apdo. postal 128, La Paz, BCS. email@example.com
2SD Herbarium, San Diego Natural History Museum, P.O. Box 121390, San Diego, CA, 92112-1390 USA. firstname.lastname@example.org
Abstract: Ambrosia humi León de la Luz and Rebman, sp. nov., a member of the Franseria alliance, is here described and illustrated. This new species is endemic to Mesa de Humí in the Sierra de La Giganta of Baja California Sur, Mexico. It is a subshrub with three lobed leaves that are gently scented and viscid when fresh, and it has a bur-like pistillate head, which is densely covered with strong aculeate spines.
Key words: Compositae, Franseria, Sierra de La Giganta, plant diversity, floristics.
Resumen: Se describe e ilustra a Ambrosia humi León de la Luz y Rebman sp. nov., un nuevo taxa de la primitiva alianza Franseria. Este nuevo taxón es aparentemente endémico de la Mesa de Humí, en la Sierra de La Giganta, en la península de Baja California, México. Se trata de una especie sub-arbustiva con hojas tri-partidas, pegajosas en fresco, ligeramente aromática, el fruto se encuentra densamente cubierto por fuertes y agudas espinas ligeramente curvadas.
Palabras clave. Compositae, Franseria, Sierra La Giganta, diversidad vegetal, florística.
Ambrosia (Asteraceae) is composed of approximately 45 species (and some varieties) that are commonly called ragweeds or bursages (Terrell et al., 1986). They grow naturally in the New World. Eight species are found outside of the Americas as naturalized weeds, according the Flora Europaea (Royal Botanic Garden, 2009) and along the northwestern coast of Africa (Lewalrée 1947). Most of the species are native to North America where some of them are considered harmful weeds because their pollen is an aeroallergen that causes hay fever. A large number of the Ambrosia species grow in desert and semi-desert conditions, some as secondary plants in ruderal or disturbed habitats. Payne (1964) and Payne et al. (1964) stated that the center of origin and diversification for this genus is in the deserts of the southwestern United States and northwestern Mexico.
Payne (1964) combined Ambrosia L. with the more diverse Franseria Cav. because the proposed characters to differentiate them were weak; although he proposed that the “ambrosioid” assemblage of species was derived from the “franserioid” group. After a review of similarities and differences between Hymenoclea Torr. & A. Gray and Ambrosia s. l. and also using molecular data on restriction sites in chloroplast DNA, Miao et al. (1995) and Strother and Baldwin (2002) concluded that the two species of Hymenoclea are most closely allied to the franserioid members of Ambrosia and should be recognized in that genus.
According to Payne (1964), several morphological characteristics show relationships between species as well as general evolutionary progressions from primitive (franserioid) to more derived characters (ambrosioid). These tendencies include the following: growth habit, from shrubby to annual; leaves, from petiolate to sessile, from alternate to opposite, from pinnately-lobed to palmately-lobed or unlobed, from dense to sparse indument, and from coriaceous to membranaceous texture; staminate capitula, from stalked to sessile, from stalked capitulous forms with more than one head to one-headed and stalked; pistillate capitula, from several florets to a single floret per capitulum; bur ornamentation, from many scattered spines to few and localized ones, and from flat to terete spines.
Rydberg (1922) recognized 15 subgeneric groups among the Ambrosia and Franseria species, but such was not accepted by Payne (1964); instead, Payne recognized four major subgeneric complexes as follows: a) The largest group comprises the majority of the franserioid species and is the more intricate in regard to evolutionary lines apparently leading from the least specialized shrubby species, such as A. dumosa (A. Gray) Payne, along at least four derivative pathways to ambrosioid species. b) A second and small group of derived taxa, made up of shrubby forms with mostly unlobed leaves having heavy glandular indumenta where A. ambrosioides (Cav.) Payne is a typical member. c) A third group of highly specialized perennial herbs and annuals is characterized by membranaceous, pinnately lobed leaves and small staminate and pistillate involucres, such as A. artemisiifolia L. d) A fourth group containing a sole derived species, A. bidentata, with sessile, unlobed leaves, one-flowered pistillate heads lacking many spines, and a highly specialized staminate involucre.
Geographically, the first group is located in the southwestern United States, the second in the less arid regions surrounding it, the third extends to central and eastern United States, and the fourth group grows only in South America. This distribution pattern provides a picture of diversification and an outward spread from the proposed center of origin.
This new taxon was first collected by Annetta M. Carter (1908-1990, UC Berkeley herbarium)) during her last botanical exploration to the Sierra de La Giganta (Baja California Sur, Mexico) in March of 1973. The specimen (A. Carter 5736) remained undescribed in the herbarium (UC 1593991) until Dr. John Strother kindly directed our attention to it and generously encouraged us to describe it, especially due to our recent, binational, floristic research in several areas of the Sierra de La Giganta (León de la Luz et al. 2008).
Ambrosia humi León de la Luz et Rebman sp. nov. Fig. 1, Fig. 2 A-G
Planta monoica perennis, suffruticosa, ad 60 cm alta. Foliis alternis, petiolatis, petiolis usque ad 5 cm longis, in caulem aliquantum decurrentibus; lamina trisecta, margine lobulata, sectione centrali grandiore, duobus lobis duas divisiones simulantibus, 8 cm longa, 6 cm lata, deltato-triangularis, supra canescens, venis principalibus prominentibus, glandulari-tomentosa, infra quam supra minus tomentosa, margine aliquantum revolutis. Capitula staminata in racemis spiciformibus, unaquaeque 15-20 floribus, pedunculis 4-6 mm longis; involucrum patelliforme 8-9 mm diam, atroviride, sparse hispidulum, 7-8 lobis triangularibus; paleae receptaculares lineari-spathulatae, villosae, 4 mm longae; corolla infundibuliformis, 4-5 mm longa, ad anthesin purpurea, postea luteola, 4 lobis; filamenta minuta, antheris magnitudinibus dissimilirabus, incurvatis; pistillum vestigiale. Capitula pistillata in glomerulis axillaribus infra racemis staminatis, 4-5 floribus, uno solum fertili, spinosis; involucrum numerosis bracteis coalescentibus, spinis puberulis in fructu immaturo. Fructus maturus sphaericus, 15-18 mm diam, 60-80 spinis robustis, 3-4 mm longis, aculeatis, basi cavitatis, sublignosis, atrantibus ubi pubescentia cadenti. Caules glandulares, in vivo viscati, in sicco laccati.
Subshrub to 60 cm tall. Stems viscid-sticky when fresh, shiny when dry. Leaves alternate, petioles to 5 cm long with decurrent blade tissue to stem, leaf blades to 8 cm long and 6 cm wide, deltate-triangular in outline, 3-lobed and each lobe divided, the central lobe the largest with 2 bigger basal lobes and often additional smaller lobes, abaxial surface canescent with main veins prominent, more glandular-tomentose than adaxial side, blade margin slightly revolute. Plants monoecious with staminate heads arranged in terminal spiciform racemes, each with 10-12 heads, each head with 15-20 flowers, peduncles 4-6 mm, involucres saucer-shaped, 8-9 mm in diameter, dark green, sparsely hispidulous, 7-8 lobes triangular; receptacular paleae linear-spatulate, villous, 3-3.5 mm long; corollas funnelform 4-5 mm long, purple at anthesis, later yellowish, four toothed; filaments small, anthers distinct, inwardly curved; pistil vestigial; pistillate heads 2-4 in axillary clusters below staminate racemose cymes, each head with 4-6 flowers, but only 1 fertile, involucre of numerous bracts fused together, puberulent and with stalked glandular hairs 3-4 mm long, fruiting involucres burlike round, 15-18 mm in diameter, bearing 60-80 strong, sharp, aculeate spines, each pitted at base and puberulent when young glabrous and darkening with age, somewhat woody at maturity.
TYPE: México, Baja California Sur: Mesa de Humí, Municipio of La Paz, 25.01136 N, -110.94598 W at 780 m, crasi-caulescent scrubland, 14 January 2008. Miguel Domínguez León 4009. (Holotype: HCIB 23216; Isotypes SD 195540, to be distributed to UC, MEXU, and IEB. Paratype, México, Baja California Sur: Mesa de Humí, Municipio of La Paz, 19 March 1973, 760 m, A. Carter 5736, UC 1593991).
Distribution and ecology. This new species is known only from Mesa de Humí, in the Municipio de La Paz, Baja California Sur, México. Plants grow in shallow, clayey soil on the summit of the mesa (750 to 820 m in elevation), where the landscape is dominated by volcaniclastic rocks of the Comondu Formation from the Miocene. Estimated surface of the mesa is approximately 1,000 hectares. Vegetation is dominated by succulent plants such as Agave sobria Brandegee, Myrtillocactus cochal (Orcutt) Britt. et Rose, Stenocereus thurberi (Engelm.) Gibson et Horak var. thurberi, Opuntia tapona Engelm., Ferocactus rectispinus (Engelm.) N.P. Taylor, Jatropha vernicosa Brandegee, and Fouquieria diguetii (Tieghem) I. M. Jhtn. Other common non-succulent plants are Prosopis palmeri S. Wats. and Ruellia californica (Rose) I. M. Jhtn. subsp. peninsularis (Rose) T. F. Daniel. In respect to the herbaceous or suffrutescent plant species, Ambrosia humi is undoubtedly one of the most common and dominant species of this area.
Phenology: Flowering during winter months, fruiting in march.
Etymology. The specific epithet for this new taxon is from “humí” a Pericú indian name for the place where it occurs.
Conservation. This taxon is rather common on this mesa and does not seem to be endangered at present because the area is difficult to access for humans and is relatively inaccessible to big herbivores such as horses and cattle, and goats do not seem to find the plants palatable.
Ambrosia humi resembles A. camphorata (Greene) Payne in respect to inflorescence, fruit type, and leaf pubescence. Ambrosia camphorata grows sporadically in western Sonora and southern Sonora, and is widespread on the Baja California peninsula where it exhibits great variability in leaf indument and pistillate head morphology. Tables 1 and 2 show general morphological features for 20 Ambrosia species (also the former Franseria and Hymenoclea) that grow naturally on the Baja California peninsula and in mainland Mexico, including this new taxon. Morphological data was taken from Shreve and Wiggins (1964), Wiggins (1980), Payne (1964), and Strother (2006), and from our specimens of the new species. In the group classification scheme according to Payne (1964), this new taxon should be incorporated into group 1.
The authors are grateful to Dr. John L. Strother, who encouraged us to describe this taxon and kindly revised the final edition of the manuscript. We would like to thanks many people who helped in several stages of preparing this manuscript such as Miguel Domínguez and Raymundo Domínguez for field work, taxonomic discussion, and information gathering, Dr. Fernando Chiang for translating our description into Latin, and Oscar Armendariz for the botanical illustration, and to the editorial team of the journal
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