ANATOMÍA Y MORFOLOGÍA

Architecture of the genus Gutierrezia (Asteraceae: Astereae, Solidagininae)

 

Silvana Gambino^1*, Francisco Ratto¹ and Adriana Bartoli¹

¹ Cátedra de Botánica Sistemática, Facultad de Agronomía, Universidad de Buenos Aires, Av. San Martín 4453, C1417DSE Buenos Aires, Argentina; sgambino@agro.uba.ar, ratto@agro.uba.ar, cbartoli@agro.uba.ar .
* Author for correspondence: S. Gambino.

---

Summary

An architectural study of the genus Gutierrezia Lag. was carried out, and seven different models were established. Differences in architecture between North American and South American species are pointed out. A key to differentiate the models is provided.

Key words: Asteraceae; Astereae; Gutierrezia; Plant architecture.

Resumen

Arquitectura del género Gutierrezia (Asteraceae: Astereae, Solidagininae)

Se llevó a cabo el estudio de la arquitectura del género Gutierrezia Lag. y se establecieron siete modelos. Se señalan las diferencias arquitecturales entre las especies de Norteamérica y Sudamérica. Se provee una clave para diferenciar los modelos propuestos.

Palabras clave: Asteraceae; Astereae; Gutierrezia; Arquitectura de plantas.

---

 

Introduction

Plant architectural studies, according to Hallé et al. (1978), Bell (1991) and Sattler (1991), have been mainly employed for describing and comparing the habit of species.
For practical reasons, a study of herbarium plants is limited to the examination of fragments and is minimally related to development. Architectural analysis can make a systematic description more complete and may provide new characters for diagnostic purposes (Tomlinson, 1987).
Architectural concepts provide several characters useful for making taxonomic decisions and whose states can be coded and usefully employed in phylogenetic analysis (Aagesen, 1999).
It is worthwhile considering architectural studies in taxonomic analysis as Bartoli & Tortosa (2003) did with genus Grindelia Willd (Asteraceae). Some years later, Bartoli (2007) conducted a phylogenetic study of Xanthocephalum group (Asteraceae, Astereae) which included morphological characters related to the architecture of plants of the genus Grindelia and related (Isocoma Nutt., Olivaea Sch. Bip. ex Benth., Rayjacksonia R. L. Hartm & M. A. Lane, Stephanodoria Greene and Xanthocephalum Willd).
Gutierrezia is a New World xerophytic genus of the tribe Asteraeae subtribe Solidagininae. It has an area of distribution in North America, where it is represented by 18 species (Nesom, 2006), it does not occur in Central America, but reappears in South America (Argentina, Bolivia, and Chile) with about 17 species (Ratto & Bartoli, 2014; 2015; 2016a, 2016b, 2016c).
The genus comprises herbaceous annuals and perennial subshrubs or shrubs that show a great variability in habit, from cushion bushes to shrubs near 1 m high, some of them developing a taproot. Also, the position of the stems varies from decumbent to erect.
The aim of the present work is to study the architecture of the species of Gutierrezia. This analysis, which leads to the setup of seven different models, may contribute –along with other morphological, cytological and molecular traits- to making taxonomic decisions.  

Material and Methods

North American species have been studied from specimens sent on loan by
PH, RSA and TEX. South American species have been observed in the field by a member of the team (FR) and others from specimens deposited in the following herbaria: BA, BAA, BAB, BBB, CONC, MCNS, MERL, LIL, LP, SI.
We also had access to digital collection of type specimens that were deposited in the following institutions: BR, COL, CORD, E, F, G, GH, GOET, K, LP, LPS, MERL, MPU, NY, P, S, SGO, US.

Results

Species of Gutierrezia are annual herbs (only from North America) or perennial ramified prostrate or erect subshrubs or shrubs up to 1 m high (North American and South American species). Representatives of the genus have sympodial shoots that end either in a solitary head (e.g. G. tortosae Ratto & A. Bartoli) or in a corymb-like or panicle-like inflorescesce [e.g. G. sarothrae (Pursh) Britton, G. taltalensis Phil.]. Heads may be pedunculate (G. mendocina Ratto & A. Bartoli) or sessile (G. chubutense Ratto & A. Bartoli).
Most perennial species have a taproot [e. g., G. isernii (Phil.) Phil.], some of them also form a crown [G. mandonii (Sch. Bip.) Solbrig, G. spathulata (Phil.) Kurtz], and in some cases they develop rhizomes [G. mendocina Ratto & A.Bartoli, G. californica (DC.) Torr. & A. Gray, G. repens Griseb.]. In Gutierrezia mandonii the herbaceous stems die after flowering season and new shoots develop afterwards from the woody base of the plant.
In the following description the terms orthotropic and plagiotropic are used as defined by Halle et al. (1978) to indicate the direction of the stems’ growth. Orthotropic stems grow vertically, while plagiotropic ones grow horizontally, over or below the soil surface.
The architectural study of the species of Gutierrezia has led to the establishment of seven different models which are described below:

MODEL 1 - Fig. 1.
Annuals. North American species of Gutierrezia.
Submodel A: Branches arise from the proximal zone of the primary stem: G. arizonica (A. Gray) M. A. Lane.
Submodel B: Proximal region of primary stem lacks branches; branching zone develops conspicuous, long internodes: G. sphaerocephala A. Gray, G.texana (DC.) Torr. & A. Gray.
Submodel C: Proximal region of primary stem lacks branches; branching zone is more condensed than the one in submodel B due to shorter internodes: G. wrightii A. Gray.

Fig. 1. Model 1, annuals, North American species. 1 A: branches arise from the proximal zone of the primary stem. 1 B: proximal region of primary stem without branches, branching zone with long internodes. 1 C: proximal region of primary stem lacks branches; branching zone with short internodes.

MODEL 2 - Fig. 2.
Perennial shrubs with taproot and orthotropic woody ramified stems that bear orthotropic herbaceous or subwoody branches. Subsequent branches are divaricated.
Submodel A: plant shape hemispherical, primary branches arise in an open angle: G. resinosa (H. & A.) Blake, G.serotina Greene, G.ramulosa (Greene) M. A. Lane.
Submodel B: plant shape conical, primary branches develop forming an acute angle: G. isernii, G. microcephala (DC.) A. Gray, G. gayana (J. Remy) Rieche.

Fig. 2. Model 2, perennial shrubs with taproot and orthotropic woody ramified stems that bear orthotropic herbaceous or subwoody branches; subsequent branches are divaricated. 2 A: plant shape hemispherical, primary branches arise in an open angle. 2 B: plant shape conical, primary branches develop forming an acute angle.

MODEL 3 - Fig. 3.
Perennial shrubs with taproot and orthotropic stems that arise from the proximal ligneous region of the plant. These leafy branches ramify in their distal part: G. sarothrae, G. grandis S. F. Blake, G. petradoria (S. L. Welsh & Goodrich) S. L. Welsh, G. pomariensis (S. L. Welsh) S. L. Welsh.

Fig. 3. Model 3, perennial shrubs with taproot and orthotropic stems that arise from the proximal ligneous region of the plant; these leafy branches ramify in their distal part.

MODEL 4 - Fig. 4.
Perennial shrubs with taproot and orthotropic stems that arise from a crown. Internodes are conspicuous and therefore secondary branches develop on distant nodes.
Submodel A: narrow crown, stems with long internodes. Stems end in solitary heads, the lower level branches are always shorter than the higher level ones: G. leucantha Cabrera.
Submodel B: narrow crown, plants more ramified and with shorter internodes than in Submodel A. Stems end in solitary heads, the lower level branches are shorter than the higher level ones: G. argyrocarpa Greenman, G.gillesii Griseb. Stems end in solitary heads, the lower level branches are longer than the higher level ones: G. solbrigii Cabrera, G. chubutense Ratto & A. Bartoli.
Submodel C: plagiotropic woody stems arising from crown which is wider and more extended than the ones described in submodels A and B. Stems end in solitary heads, the lower level branches are shorter than the higher level ones: G. spathulata.

Fig. 4. Model 4, perennial shrubs with taproot and orthotropic stems that arise from a crown; internodes are conspicuous; therefore secondary branches develop on distant nodes; stems end in solitary heads. 4 A: narrow crown, stems with long internodes; the lower level branches are always shorter than the higher level ones. 4 B: narrow crown, plants more ramified and with shorter internodes than in A; the lower level branches may be shorter or longer than the higher level ones, depending on the species. 4 C: plagiotropic woody stems arising from crown which is wider and more extended than the ones described in submodels A and B; the lower level branches are shorter than the higher level ones.

MODEL 5 - Fig. 5.
Perennial shrubs with taproot and long decumbent stems. Lower order stems are shorter (*) or longer (**) than the higher order ones, depending on the species.
Submodel A: both plagiotropic and orthotropic branches developing from the woody base of the plant: G. taltalensis (**), G. mandonii (**), G. espinosae Acevedo (*).
Submodel B: decumbent stems arise from primary axis and spread radially. These underground plagiotropic stems (rhizomes) develop adventitious roots: G.mendocina (**), G. californica (**), G. repens (*), G. alamani A. Gray var. alamani (**), G. alamani var. megalocephala (Fernald) M. A. Lane. (*), G. conoidea (Hemsl.) M. A. Lane (*).

Fig. 5. Model 5, perennial shrubs with taproot and long decumbent stems; lower order stems are shorter or longer than the higher order ones, depending on the species. 5 A: both plagiotropic and orthotropic branches developing from the woody base of the plant. 5 B: decumbent stems arise from primary axis and spread radially; these rhizomes develop adventitious roots.

MODEL 6 - Fig. 6.
Perennial shrubs with taproot. Orthotropic, scarcely branched leafy 2nd and higher order stems that end in solitary heads: G. tortosae.

Fig. 6. Model 6, perennial shrubs with taproot; orthotropic, scarcely branched leafy second and higher order stems that end in solitary heads.

MODEL 7 - Fig. 7.
Perennial rhizomatous cushion bushes. Decumbent stems with short internodes, ending in sessile to subssessile heads: G. baccharoides Sch. Bip., G.ameghinoi.Speg.

Fig. 7. Model 7, perennial rhizomatous cushion bushes; decumbent stems with short internodes, ending in sessile to subssessile heads.

Key
A- Annuals.
B- Branches arising from the proximal zone of the primary stems. .......................... Model 1 Submodel
BB- Proximal region of primary stems without branches.
C- Branched zone developing conspicuous, long internodes. .............................Model 1 Submodel B
CC- Branched zone without conspicuous internodes. ........................................ Model 1 Submodel C
AA- Perennials.
D- Cushion bushes. Decumbent stems with short internodes, ending in sessile heads. ................. Model 7
DD- Shrubs or subshrubs with taproot, not cushion bushes.
E– Perennial shrubs with only orthotropic stems.
F- Orthotropic stems arising from a crown.
G- Narrow crown.
H- Long internodes, plants loosely branched. Stems ending in solitary heads, lower level branches always shorter than the higher level ones. .................... Model 4 Submodel A
HH- Internodes short. ............................................................................ Model 4 Submodel B
GG- Wide crown. ...................................................................................... Model 4 Submodel C
FF- Primary branches arise from the proximal ligneous region of the plant, crown absent.
I- Second and higher order divaricated branches developing at distant scattered nodes. . Model 2
II- Second and higher order branches develop not like in I.
J- Orthotropic, scarcely branched leafy 2nd and higher order stems ending in solitary sessile heads. Hemispherical plants, broom-like when herborized. ..................... Model 6
JJ- Orthotropic stems arising from the proximal woody region of the plant. These leafy branches ramified at their distal part forming a corymb like inflorescence. ........... Model 3
EE- Perennial shrubs with orthotropic and plagiotropic stems.
K- Plagiotropic and orthotropic branches developing at the base of the plant. . Model 5 Submodel A
KK- Decumbent stems arising from primary axis and spreading radially. Underground plagiotropic stems (rhizomes) developing adventitious roots. ......... Model 5 Submodel B

Discussion

Species of Gutierrezia show variations in plants architecture. It comprises herbs, subshrubs or shrubs with morphological adaptations to the xerophytic habitats. Rhizomes, woody stems with taproots, very small and narrow leaf blades and root systems several times larger than the aerial portion are adaptive strategies to handle stress, fire and herbivory (Bartoli & Tortosa, 2003).
Some North American species of Gutierrezia are annuals (Model 1) or perennial subshrubs or shrubs (Models 2 to 5), with renewal buds located on the stems, above or under the ground (Model 5) or on woody old branches (Model 2 to 4). The annual models are found only in North American species.
Rhizomatous or stolonifer species (Model 5) and species with taproot (Model 2 to 5) are present in North and South America. On the other hand, perennial cushion subshrubs are present only in South America (Model 7), as well as plants with taproot and orthotropic stems.

Conclusions

The study of the architecture of plants of the genus Gutierrezia and all the characters involved in this analysis could be useful in phylogenetic studies. We conclude that an architectural analysis provides more diagnostic characters which can be coded in order to contribute to making taxonomic decisions.

Bibliography

1. AAGESEN, L. 1999. Phylogeny of the tribe Colletieae, Rhamnaceae. Bot. J. Linn. Soc. 131: 1-43.         [ Links ]

2. BARTOLI, A. 2007. Revisión taxonómica, análisis cladístico y biogeográfico del grupo Xanthocephalum (Asteraceae, Astereae, Machaerantherinae). Tesis presentada para optar al título de Doctor en Ciencias Naturales de la Facultad de Ciencias Naturales y Museo Universidad Nacional de La Plata. Argentina.         [ Links ]

3. BARTOLI, A. & R. D. TORTOSA. 2003. Architecture of the genus Grindelia (Asteraceae: Astereae). Flora 198: 106-111.         [ Links ]

4. BELL, A. D. 1991. Plant Form: An illustrated guide to Flowering Plant Morphology. Oxford, U.K: Oxford University Press.         [ Links ]

5. HALLÉ, F., R. A. A. OLDEMAN & P. B. TOMLINSON. 1978. Tropical trees and forests: an architectural analysis. Springer-Verlag, Berlin.         [ Links ]

6. NESOM, G. L. 2006. Grindelia. En Flora of North America Editorial Committee (Ed.). Flora of North America North of Mexico, 20: 424-436. Oxford University Press, Oxford.         [ Links ]

7. RATTO, F. & A. BARTOLI. 2014. Gutierrezia mendocina (Asteraceae, Astereae), a new South American species. Collectanea Botanica 33: e002. doi: http://dx.doi.org/10.3989/collectbot.2013.v33.002         [ Links ]

8. RATTO, F. & A. BARTOLI. 2015. The resurrection of Gutierrezia ameghinoi Speg. (Asteraceae, Astereae, Solidagininae), a species from Patagonia Argentina. Phytotaxa 220: 295-300.         [ Links ]

9. RATTO, F. & A. BARTOLI. 2016a. Una nueva especie de Gutierrezia (Asteraceae, Astereae) de Argentina. Collectanea Botanica. 35: e004. doi: http://dx.doi.org/10.3989/collectbot.2016.v35.004         [ Links ]

10. RATTO, F. & A. BARTOLI. 2016b. A new species of Gutierrezia (Asteraceae, Astereae, Solidagininae) from Argentinian Patagonia. Phytotaxa (in press).         [ Links ]

11. RATTO, F. & A. BARTOLI 2016c. Reinstatement of Gutierrezia leucantha Cabrera (Asteraceae, Astereae). Webbia (in press).         [ Links ]

12. SATTLER, R. 1992. Process morphology: structural dynamics in development and evolution. Can. J. Bot 70: 708-714.         [ Links ]

13. TOMLINSON, P. B. 1987. Architecture of tropical plants. Ann. Rev. Ecol. Syst. 18: 1-21.         [ Links ]

14. TORTOSA, R.D., L. AAGESEN & G.M. TOURN. 1996. Morphological studies in the tribe Colletieae (Rhamnaceae): analysis of architecture and inflorescences. Bot. J. Linn. Soc.: 122: 353-367.         [ Links ]

Recibido 21 de marzo de 2016,
aceptado 6 de mayo de 2016.