Taxonomía y florística

 

A new Ambrosia (Asteraceae) from the Baja California Peninsula, Mexico

 

Una nueva Ambrosia (Asteraceae) de la Península de Baja California, México

 

José Luis León de la Luz^{1, 3} and Jon P. Rebman²

 

¹ Herbario, Centro de Investigaciones Biológicas del Noroeste. ³ Autor para la correspondencia: jlleon04@cibnor.mx

² San Diego Natural History Museum.

 

Received: September 7,2009.
Accepted: December 10, 2009.

 

Abstract

Ambrosia humi León de la Luz et Rebman, sp. nov., a member of the Franseria alliance, is here described and illustrated. This taxon is apparently endemic only to Mesa de Humí in the Sierra de La Giganta of Baja California Sur, Mexico. This new species is a subshrub with three–parted leaves that are gently scented and viscid when fresh, and it has a bur–like pistillate head, at maturity it is densely covered with strong, sharp, 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.

 

The genus Ambrosia (Asteraceae) is composed of approximately 45 species (and some varieties) that are commonly called ragweeds or bursages. They grow naturally in the New World, but two species are found outside of the Americas in southern Europe and along the western 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) state 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 the small genus 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. Recently, 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, both 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 petiolated to sessile, from alternate to opposite, from pinnately–lobed to palmately–lobed or un–lobed, from dense pubescence to less pubescent, 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 spines to terete.

Rydberg (1922) recognized 15 subgeneric groups among the Ambrosia and Franseria species, but such was not accepted by Payne (1964); instead, he recognized only 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 northern and eastern North America, 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) 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 unde–scribed for several years in the university of California at Berkeley 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. Figure 1, Figure 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 linearispathulatae, villosae, 4 mm longae; corolla infundibuliformis, 4–5 mm longa, ad anthesin purpurea, postea luteola, 5 lobis; stamina monadelpha, 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 that remains as shiny shellac when dry. Leaves alternate, petioles up to 5 cm long with decurrent blade tissue to stem, leaf blades up to 8 cm long and 6 cm wide, deltate–triangular in outline, deeply three–divided and each division lobed, the central division the largest with two 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 spici–form racemes, each with 10–12 heads, each head with 15–20 flowers, head peduncles 4–6 mm, involucres saucer–shaped and 8–9 mm in diameter, dark green, sparsely hispidulous, 7–8 triangular lobes; receptacular paleae linear–spatulate, villous, 3–3.5 mm long; corollas funnelform 4–5 mm long, purple at anthesis, later yellowish, five toothed, filaments monodelphus; anthers distinct, inwardly curved; pistil vestigial; pistillate heads 2–4 in axillary clusters below staminate racemes, each head with 4–6 flowers, but only one fertile, bur–like, involucre of numerous bracts fused together, with puberulent and stalker glandular hairs 3–4 mm long, fruiting involucres round, 15–18 mm in diameter, bearing 60–80 strong, sharp, aculeate spines, each pitted at base and puberulent when young but 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 deliver to UC, MEXU, and IEB. Paratype, México, Baja California Sur: Mesa de Humí, Municipio of La Paz, 19 March 1973, 750 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. The population grows only on the summit of the mesa (760 to 820 m in elevation), where the landscape is dominated by volcaniclastic rocks of the Comondu Formation from the Miocene where plants grow in a shallow, clayey soil. Estimated surface of the mesa is approximately 1000 hectares. Vegetation is dominated by succulent plants such as Agave sobria Brandegee, Myrtillo–cactus 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. Population of this taxon is rather common on this mesa and does not seem to be endangered at this moment since 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.

 

Discussion

Ambrosia humi has some resemblance to A. camphorata (Greene) Payne in respect to inflorescence, fruit type, and leaf pubescence. A. camphorata grows sporadically in western sonora and southern sonora, but is widespread on the Baja California peninsula where it exhibits great variability in leaf pubescence and pistillate head morphology. Table 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 northwestern Mexico, including this new taxon. Morphological data was taken from Shreve and Wiggins (1964), Wiggins (1980), Payne (1964), Strother (2006), and from our voucher specimens of the new species. In the group classification scheme according to Payne (1964), this new taxon should be incorporated into "group 1", i.e., that basal group of franserioid species geographically located on the southwestern United States and adjacent areas.

 

Acknowledgements

The authors are grateful to Dr. John L. Strother, who encouraged us to describe this taxon. 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.

 

Literature cited

León de la Luz J.L., Rebman J., Domínguez–León M. and Domínguez–Cadena R. 2008. The vascular flora and floristic relationship of the Sierra de La Giganta in Baja California Sur, México. Revista Mexicana de Biodiversidad. 79:29–65        [ Links ]

Lawalrée A. 1947. Les Ambrosia adventice en Europe occidentale. Bulletin Jardin. Botanique des Bruxelles 18:306–315.         [ Links ]

Miao B., Turner B., Simpson B., and Mabry T. 1995. Chloroplast DNA studies of the genera Ambrosia s. l. and Hymenoclea (Asteraceae): systematic implications. Plant Systematic and Evolution 194:241–255.         [ Links ]

Payne, W.W. 1964. A re–evaluation of the genus Ambrosia (Compositae). Journal of the Arnold Arboretum. 45:401–438.         [ Links ]

Payne W.W., Raven PH., and Kyhos D.W. 1964. Cromosome numbers in Compositae. IV Ambrosieae. American Journal of Botany 51:419–424.         [ Links ]

Rydberg PA. 1922. Ambrosiaceae. North American Flora 33: 3–44.         [ Links ]

Shreve F. and Wiggins I.L. 1964. Vegetation and Flora of the Sonoran Desert, Vol 1. Stanford University Press. Stanford, Cal.         [ Links ]

Strother, J.L. 2006. Ambrosia. En: Flora of North America Editorial Committee eds. Flora of North America: North of Mexico vol 21 Magnoliophyta: Asteridae, Part 8: Asteraceae, Part 3 pp. 10–18. Oxford University Press. USA.         [ Links ]

Strother, J.L. and Baldwin, B.G. 2002. Hymenoclea are ambrosias (Compositae). Madroño 49:143–144.         [ Links ]

Wiggins, I.L. 1980. Flora of Baja California. Stanford University Press. Stanford.         [ Links ]