Heteranthera catharinensis C.N.Horn & M.Pell., 2017

Pellegrini, Marco O. O. & Horn, Charles N., 2017, Two peculiar new species of Heteranthera Ruiz & Pavon (Pontederiaceae) from Brazil, with notes on inflorescence architecture in the family, PhytoKeys 82, pp. 35-56 : 35

1. Heteranthera catharinensis C.N.Horn & M.Pell. sp. nov. Figs 1 , 2 , 3

Diagnosis.

Similar to Heteranthera reniformis Ruiz & Pavón due to is petiolate leaves with reniform to broadly cordate blades, glandular-pubescent cincinnus axis, perianth lobes with a 5+1 arrangement, and straight filaments. It is unique due to its 3.2-5.5 cm long, glabrous peduncles, basal bract with spatulate-mucronate apex, 6-17-flowered, glomerulate cincinnus; externally glabrous perianth lobes, central superior perianth lobe 6.6-9.2 mm long, central stamen with glabrous filament, lateral anthers 1-1.8 mm long, central anther 1.7-2.4 mm long, and glabrous style.

Type.

BRAZIL. Santa Catarina: Ipumirim, 4-7 km south of the Rio Irani , 26°59'S, 52°11'W, alt. 500-600 m, 9 Dec 1964, L.B. Smith & R.M. Klein 13919 (holotype: US barcode US01936706!; isotypes: FLOR barcode FLOR3365!, LP!, MO!, NY!, R!) .

Description.

Herbs annual or short-lived perennials. Roots thin, delicate, unbranched, white. Stems repent on the substrate or floating in shallow water, delicate, spongy, rooting at the nodes; internodes 1.6-4.3 cm long, glabrous. leaves not seen. Petiolate leaves distichously-alternate, distributed along the stem, floating to emergent; sheaths 2.6-5.5 cm long, glabrous, covered with mucilage, longitudinally split and green when mature, ligule 2-parted, barely surpassing the sheath, 0.1-0.3 mm long, membranous, light green, glabrous, apex triangular; petiole 3.3-21 cm long, not inflated, glabrous; blades 1.3-3.3 × (1.4-)3-4.6 cm, reniform to broadly cordate, membranous, glabrous, base cordate, margins glabrous, apex obtuse to slightly acute. Inflorescences axillary or apparently terminal, reduced to a solitary pedunculate cincinnus; peduncle 3.2-5.5 cm long, glabrous; basal bract (spathe) 1.6-3.3 × 0.3-0.5 cm, spathaceous, elliptic, conduplicate, glabrous, green, margins hyaline, apex spatulate-mucronate; cincinnus bract absent; cincinnus 6-17-flowered, flowers congested at the base and apex of the cincinnus, 1-2 flowers included in the basal bract, axis 3-6.5 cm long, slightly to densely glandular-pubescent. Flowers bisexual, tubular, chasmogamous, sessile, enantiostylous; floral buds narrowly ellipsoid, light green, glabrous; perianth tube 5-7.5 mm long, light green, glandular-pubescent, lobes 5 superior and 1 inferior, white, lateral superior lobes 6.6-8.3 × 1.2-2.5 mm, elliptic, base cuneate, apex acute to acuminate, central superior lobe 6.6-9.2 × 1.6-2.5 mm, ovate to broadly ovate, base obtuse, slightly involute, apex acute, with a nectar guide at base, pale to medium yellowish green with an upper mauve to vinaceous spot, inferior lobe 6.5-9.5 × 0.4-1 mm, linear elliptic, base cuneate, apex acuminate; stamens 3, lateral stamens with filaments straight, 1.5-2 mm long, not inflated, apically barbate with eglandular, multi-celled hairs, anthers 1-1.8 × 0.3-0.4 mm, oblongoid to ellipsoid, yellow, central stamen with filament straight, 3-3.6 mm long, not inflated, glabrous, anthers 1.7-2.4 × 0.4-0.6 mm, ovate to slightly sagittate, white; ovary 3.2-3.8 × 1.1-1.3 mm, linear ovoid to linear oblongoid, glabrous, 1-locular, placentation intrusive-parietal, style gently sigmoid, 5.1-9.3 mm long, glabrous, stigma unevenly trilobate, densely glandular-pubescent. Capsules not seen; persistent perianth base (anthocarp) smooth, medium brown. Seeds not seen.

Specimens seen

(paratypes). BRAZIL. Santa Catarina: Caçador, slough, 33 km W of Caçador, fl., 23 Dec 1956, L.B. Smith & R. Reitz 9103 (HBR!, NY!, P barcode P02188433!, US barcode US01936705!)

Etymology.

The epithet makes reference to the type locality, the state of Santa Catarina, Brazil.

Distribution, habitat and ecology.

Heteranthera catharinensis is currently endemic to the state of Santa Catarina, in the Atlantic Forest domain (Fig. 3 ). Is was found growing on open marshy areas and slow water environments within the Uruguay River watershed.

Phenology.

Heteranthera catharinensis can be found in bloom in December. Unfortunately, neither of the two currently known collections present mature fruits, thus fruiting time remains unknown.

Conservation status.

Following the IUCN recommendations ( IUCN 2001), H. catharinensis should be considered as Data Deficient (DD), since it is known from only two collections, which are more than 50 years old.

Morphological notes.

The inflorescence of H. catharinensis is extremely peculiar, meriting explanation. The glomerulate appearance of the inflorescence (i.e. flowers congested at the base and apex of the inflorescence) seems to be due to changes in the length of the cincinnus internodes. The first one to three internodes are contracted, similarly to most species in the genus, thus making the basalmost flowers to be partially enclosed by the basal bract. Nonetheless, the following internode is considerably and consistently elongated, being commonly three to five times longer than the previous internodes. The subsequent internodes are also contracted, giving the impression that the flowers are also congested at the apex of the inflorescence. This alternation between contracted and elongated internodes, produces a unique inflorescence architecture in the genus (Fig. 2B ).

Affinities.

Heteranthera catharinensis is morphologically similar to H. reniformis s.s. due to its petiolate leaves with reniform to broadly cordate blades, pedunculate inflorescences, cincinnus axis glandular-pubescent, glandular-pubescent perianth tube, perianth lobes with a 5+1 arrangement and acute to acuminate at apex, lateral stamens apically barbate, and intrusive-parietal placentation ( Horn 1985). It is also superficially similar to H. multiflora s.l. due to its bigger stature, many-flowered inflorescence with few flowers included in the basal bract, and gross floral morphology ( Horn 1985). Nonetheless, H. catharinensis can be easily differentiated from all remaining species of Heteranthera by its unique inflorescence architecture (where flowers are congested at the base and the apex of the cincinnus), larger flowers size, numerous flowers on an elongate axis, main axis many times longer that the basal bract, and basal bract with spatulate-mucronate apex. Aside from that, specimens of H. catharinensis have been erroneously identified as H. peduncularis Benth, due to their robust habit and long inflorescences. However, both species can be easily differentiated based on inflorescence architecture, and pubescence of the tepals and filaments. Furthermore, H. catharinensis has larger floral features, when compared to the remaining species of the H. reniformis complex, including longer perianth lobes and larger anthers. It is also the only species in the complex with externally glabrous perianth lobes, and glabrous central filament and style (Table 1 ).

Figures

Figure 1. Holotype of Heteranthera catharinensis C. N. Horn & M. Pell. Image courtesy of the Smithsonian Institution, NMNH, US herbarium.

Figure 2. Line drawing of Heteranthera catharinensis C. N. Horn & M. Pell. A Detail of the leaf blade B Detail of the apex of the stem, showing the ligule and an inflorescence at anthesis C Detail of the basal bract, showing the spatulate-mucronate apex D Glandular hair from the cincinnus axis and floral tube E Dissected perianth lobes, showing the 5 + 1 arrangement F Lateral stamen G Uniseriate hair from the lateral stamen H Central stamen I Gynoecium, showing the glabrous style and unevenly trilobate stigma. Illustration by M. O. O. Pellegrini, based on the paratype (Smith & Reitz 9103, US).

Figure 3. Distribution map. ■ Heteranthera catharinensis C. N. Horn & M. Pell. ● H. pumila M. Pell. & C. N. Horn. Green- Parana watershed; Yellow- Uruguay watershed; Red- Southeastern Atlantic watershed; following ANA - Agencia Nacional de Aguas (2002).