Chromolaena congesta (Hooker & Arnott) R.M. King & H. Robinson (1970: 200)

Christ, Anderson Luiz & Ritter, Mara Rejane, 2019, A taxonomic study of Praxelinae (Asteraceae-Eupatorieae) in Rio Grande do Sul, Brazil, Phytotaxa 393 (2), pp. 141-197 : 154-158

2.3. Chromolaena congesta (Hooker & Arnott) R.M. King & H. Robinson (1970: 200) .

Eupatorium congestum Hooker & Arnott (1836: 239) . Lectotype (designated by Freire & Ariza Espinar 2014b: 339):— URUGUAY. s.l., s.d., J. Tweedie s.n. (E! [E00385502], isolectotypes E! [E00385501], GH! [GH00007606], K! [K000486826]).

= Eupatorium bracteatum Hooker & Arnott (1836: 239) . Type:— URUGUAY. s.l., s.d., J. Tweedie s.n. (holotype K! [K000486827, isotype GH! [GH00007564]).

= Eupatorium tozziifolium Candolle (1836: 146) . Type:— BRAZIL. São Paulo, 1833, C. Gaudichaud 504 (holotype P! [P00742705]). ( Fig. 8A–E , 9A–C ).

Subshrubs, up to 30 cm tall, erect to rarely decumbent, xylopodium present, branched from base or only in capitulescence; stems strigose to tomentose, rarely hirsute, glandular or rarely eglandular, leafy until capitulescence. Leaves 0.7–3.5 × 0.5–2.2 cm, opposite, petiolate, 3-veined, leaf blade ovate to lanceolate, sometimes deltate, chartaceous to coriaceous, apex acute to obtuse, base rounded to truncate, rarely cordate, margins crenate, adaxial surface glabrescent to strigose, glandular or eglandular, abaxial surface strigose, glandular, margins ciliate, petioles 1.2–3.4 mm long, strigose to hirsute, glandular. Primary capitulescences glomeruliform or sometimes corymbose. Secondary capitulescences corymbose, axis strigose to tomentose, rarely hirsute, glandular, bracteate or ebracteate, bracts 0.3–2 × 0.1–1.1 cm, sometimes with margins entire, petioles 1–1.8 mm long, strigose, glandular or eglandular. Capitula sessile to subsessile, peduncles up to 0.4 cm long, puberulous to tomentose, glandular, involucres cylindrical, 5.3–8.1 × 2–3.5 mm, involucral bracts 15–23, 4–6-seriate, outer ovate to oblong, 2–3.3 × 1–2.1 mm, apex cuneate to truncate, rarely acuminate, citrine to vinaceous, ciliate, puberulous, glandular, recurved to slightly recurved, abaxial surface stramineous to citrine, 3–5-veined, glabrous to puberulous, inner linear, 4.3–7.2 × 0.7–1.2 mm, apex acute to acuminate, citrine to vinaceous, non-petaloid, ciliate, puberulous, glandular, recurved to slightly recurved, abaxial surface stramineous to citrine, 1–3 veined, glabrous, receptacles epaleate or rarely paleate, palea 0–1, linear, 6.5–6.6 × 0.6–0.7 mm, 1-veined, apex and abaxial surface stramineous, ciliate, glandular. Florets 5–11, corollas 3.6–5.6 × 0.5–0.9 mm, lilac, lobes glabrous to puberulous, glandular to rarely eglandular. Cypselas obconical, 2.4–3.3 × 0.5–0.8 mm, 5–8-ribbed, ribs setuliferous, sinuses glabrous to setuliferous, glandular or rarely eglandular, pappus setae ca. 30–47, stramineous, 3.8–5.5 mm long.

Distribution: — Argentina , Brazil, Paraguay and Uruguay ( Freire & Ariza Espinar 2014b). In Brazil, it occurs in Minas Gerais, Paraná, Rio Grande do Sul, Santa Catarina and São Paulo. In Rio Grande do Sul, it occurs in the physiographic regions of Alto Uruguai, Campos de Cima da Serra, Depressão Central, Encosta Inferior do Nordeste, Encosta Superior do Nordeste and Planalto Médio ( Fig. 10 , triangles).

Habitat: —Grasslands in both Atlantic Forest and Pampa, being more common in the former.

Phenology: —Flowers from the end of summer to the beginning of autumn, with a flowering peak from February to April.

Etymology: —Latin congestus (aggregated, agglomerated), with reference to the dense capitulescences.

Comments: — Chromolaena congesta is one of the most common species of Chromolaena in grasslands in Southern Brazil, particularly in regions of occurrence of the Atlantic Forest biome, as in the case of the northern half of Rio Grande do Sul. The species is fairly common in its localities, despite showing a tendency of forming sparse populations with scattered individuals.

Taxonomically, C. congesta is probably the species of Chromolaena found in Rio Grande do Sul with the most problematic circumscription and the most challenging identity. This is due to the incosistent treatments it received from different authors since its original description, but also due to an apparent lack of strong diagnostic features. Hooker & Arnott (1836) emphasized the shape and indumentum of the leaves and the well-marked veins in the abaxial surface of the leaves, but these characters tend to vary greatly in the studied populations. Also, these characters (as well as many others, such as the indumentum and shape of the involucral bracts, indumentum of cypselas and number of florets) more or less form a gradient between C. congesta and a number of similar species occurring in the same geographical range and in similar habitats. This group of species is here informally named “ Chromolaena congesta group” and is the subject of several identifications problems in the examined material and discordant taxonomic treatments according to different authors. The existence of a morphological continuum bonding C. congesta to the other species of the group greatly threatens their identification, particularly of C. congesta . It is clear that further studies using a deeper, integrative approach are needed to completely understand the boundaries of these species and to allow a better and easier identification. The species considered as part of the group are summarized in Table 1, along with their most recurring synonyms and their geographical range.

Among the species of the group found in Rio Grande do Sul, C. congesta is particularly similar to C. hirsuta and C. latisquamulosa . It differs from the former mostly by the always opposite leaves (vs. almost always alternate, rarely opposite leaves), the crenate margins of the leaves (vs. leaves with entire margins on apical half and crenate or serrate in basal half) and the indumentum, which is only rarely hirsute (vs. mostly hirsute). There are a number of specimens with intermediary morphology between both species, and the relationship between them remains unclear. Malme (1933) has indicated the existence of supposed hybrids between C. congesta and C. hirsuta , but this hypothesis could not be tested in this study. In any case, the phyllotaxy is still the best morphological character useful to distinguish them. Chromolaena congesta differs from C. latisquamulosa by the usually erect habit (vs. usually decumbent habit), the denser indumentum of stems, leaves and involucral bracts and the presence of glandular hairs in the abaxial surface of the leaves (vs. abaxial surface of the leaves always eglandular).

We disagree with Cabrera (1996) and Freire & Ariza Espinar (2014b), who considered C. congesta and C. ascendens (Sch.Bip.) R.M.King & H. Rob. as synonymous with C. squarrulosa . The reason for this is mainly the characteristic indumentum and shape of the involucral bracts in C. squarrulosa , which bear a tomentose, recurved to (mostly) squarrose apex. This character was not recorded in any other species occurring in the study area, and, despite the existence of a morphological continuum regarding the vegetative characters between these species, remains a discontinuity with regard of characters mentioned above.

Chromolaena ascendens is a species typical of the Southeastern region of Brazil, mainly in Minas Gerais and São Paulo, and does not occur in Rio Grande do Sul. Despite this, a number of specimens analyzed in this study were labeled as C. ascendens , most of them corresponding to varying morphotypes of C. congesta or C. latisquamulosa . Chromolaena ascendens can be distinguished from C. congesta and C. latisquamulosa mostly through the tomentose indumentum of stems and abaxial surfaces of the leaves, the greater number of florets, the smaller dimensions of the capitula, cypselas and pappus and the fewer number of setae in the pappus.

Chromolaena congesta is also very similar to C. caaguazuensis (Hieron.) R.M.King & H. Rob. , a species not yet recorded in Brazil. Chromolaena caaguazuensis can be identified by its pendant leaves with cordate base, fewer numbers of florets and somewhat denser cover of glandular hairs in the abaxial surface of the leaves and involucral bracts.

Specimens examined: — BRAZIL: Rio Grande do Sul: Arroio do Meio: Morro Gaúcho [29°20’14,08’’S, 51°55’58,24’’W], 06 February 2011, Bruisma, G. 179 ( HVAT). Arroio dos Ratos: Granja Faxinal, 15 March 1976, Hagelund, K. 10111 ( ICN). Barros Cassal: entre Barros Cassal e Vila Costa, 19 March 1978, Reis, I. 285 ( ICN). Bom Jesus: Fazenda Caraúna, March 1936, Dutra , J. 1255, 1270 ( ICN) ; Rio dos Touros, 13 January 1942, Rambo, B. s.n. ( PACA8585 ) ; s.l., 25 March 2017, Christ, A. L. 402 ( ICN) ; 25.III.2017, Christ, A. L. 413 ( ICN). Cambará do Sul: Itaimbezinho , 20 February 1953, Rambo, B. s.n. ( PACA53952 ) ; 12 February 1956, Rambo, B. s.n. ( PACA59249 ) ; RS-439, 1 March 2010, Hattori, E. K. O., Dettke, G. A., Welker, C. D. & Ferreira, P. A. 1108 ( BHCB). Canela: Passo do Inferno , 11 April 2005, Bordignon, S. & Apel, M. 3096 ( ICN). Carazinho: s.l., February 1944, Augusto, I. s.n. ( ICN18038 ). Caxias do Sul: Forqueta, 10 February 1989, Wasum, R. s.n. ( HUCS5316 ) ; Ana Rech, Faxinal , 06 January 1992, Wasum, R. et al. s.n. ( HUCS8052 ) ; Vila Seca , 12 January 2000, Scur, L. 379 ( HUCS) ; Criúva , 25 February 2000, Scur, L. 700 ( HUCS, MBM) ; Ana Rech , 19 March 2000, Kegler, A. 855 ( HUCS, MBM) ; 13 April 2013, Gaio, J. & Keil, R. 338 ( HUCS) ; Criúva, Cânion dos Palanquinhos, 04 February 2017, Gonzatti, F. 3357 ( HUCS). Cruz Alta : s.l., January 1944, Verissimo, C. A. s.n. ( PACA25518 ) ; Fumagali , 24 January 1975, Arzivenco, L. s.n. ( ICN45338 ). Erechim: BR-153, 25 January 1995, Butzke, A. & Nodani, M. s.n. ( HUCS11488 ). Esmeralda: s.l., 17 February 1979, Arzivenco, L. 590 ( ICN). Giruá: Granja Sodal, March 1964, Hagelund, K. 1790 ( ICN). Guaíba: Fazenda São Maximiano, 24 February 1975, Matzenbacher, N. I. 158 ( ICN) ; 30 April 1975, Ramos, R. s.n. ( ICN29494 ) ; 01 February 1978, Matzenbacher, N. I. s.n. ( ICN176875 ) ; 25 December 1978, Matzenbacher, N. I. s.n. ( ICN43614 ). Jaquirana: Propriedade do Seu Ângelo [29°01’S, 50°24’W], 18 March 2017, Christ, A. L. 378, 379 ( ICN). Jari: entre Jari e Quevedos, 08 March 2015, Christ, A. L. 42 ( SMDB). Julio de Castilhos : Passo do Felício , 15 February 1994, Mondin, C. 856 ( ICN). Lagoa Vermelha: proximidades do rio Uruguai , January 1943, Friderichs, E. s.n. ( PACA11442 ). Marcelino Ramos: Estreito Rio Uruguai , 04 November 1993, Butzke, A. et. al. s.n. ( HUCS11880 ). Porto Alegre: Montserrat, 01 April 1942, Emrich, K. s.n. ( PACA28939 ) ; Morro das Abertas , 09 January 1949, Rambo, B. s.n. ( PACA39647 ) ; Montserrat , 14 March 1949, Emrich, K. s.n. ( PACA40533 ) ; Vila Manresa , 03 March 1950, Rambo, B. s.n. ( PACA40364 ) ; Morro Santana , 24 March 1969, Irgang, B. & Hemrich, M. s.n. ( ICN5802 ) ; Parque Saint-Hilaire , 17 March 1982, Santos, M. s.n. ( ICN53372 ) ; Morro do Osso , 24 January 1996, Rodrigues, R. S. 265 ( ICN) ; Morro Santana , 28 April 2005, Longhi-Wagner, H. & Welker, C. 9759 ( ICN) ; [30°03’40,3’’S, 51°07’25,6’’W], 20 April 2007, Fernandes, A. C. & Ritter, M. R. s.n. ( ICN158453 ) ; [30°03’10,3’’S, 51°07’44’’W], 09 May 2008, Fernandes, A. C. & Ritter, M. R. s.n. ( ICN158455 ) ; 17 March 2017, Christ, A. L. 394, 396 ( ICN) ; Morro São Pedro, 25 March 2017, Christ, A. L. 358, 361, 362, 363, 369, 372, 373 ( ICN). Santa Maria: Morro Pedra do Lagarto , Distrito de Santo Antão , 04 March 2015, Schaefer, J. 418 ( SMDB) ; Campo de Instrução de Santa Maria, 17 April 2015, Christ, A. L. 104 ( SMDB). São Francisco de Paula : RS-235, 27 February 2000, Wasum, R. 463 ( HUCS) ; Linha São Paulo, 10 February 2002, Wasum, R. 1320, 1323 ( HUCS) ; Lajeado Grande , 04 March 2003, Wasum, R. et. al. 1818 ( HUCS, MBM). São José dos Ausentes: s.l. [28°31’20,80’’S, 49°59’20,80’’W], January 2002, Sobral, M. et. al. 9511 ( ICN) ; Fazenda Pedra Moura , 08 April 2002, Wasum, R. & Sobral, M. 1447 ( HUCS, MBM) ; 06 April 2011, Schmitt, J. L. 3156 ( FURB). Tupanciretã: Rio Ijuizinho, 30 January 1942, Rambo, B. s.n. ( PACA4965 ). Viamão : s.l., 10 April 1950, Rambo, B. s.n. ( PACA46722 ) ; Parque Saint-Hilaire , 03 February 1967, Baptista , L. R. M. & Irgang, B. E. s.n. ( ICN8039 ) ; Bairro Tarumã, região de entorno do lago Tarumã [30°4’1,34’’S, 51°1’20,55’’W], 15 March 2009, Silva Filho, P. J. S. 793 ( ICN) .

Figures

FIGURE 8A–E: Chromolaena congesta. A. Fertile specimen. B. Capitulum. C. Involucral bracts. D. Floret. E. Palea. F–J: Chromolaena elliptica. F.Fertile specimen. G. Capitulum. H. Involucral bracts. I. Floret. J. Xylopodium.

FIGURE 9A–C: Chromolaena congesta. A. General view. B. Primary capitulescence. C. Xylopodium. D–F: Chromolaena elliptica. D. Primary capitulescence. E. Leaves. F. General view. Credits:Anderson Christ (A–F).

FIGURE 10: Distribution of C. congesta (triangles) and C. elliptica (circles) in Rio Grande do Sul.