Phyllanthus pterocaulis M.J. Silva, 2022

Silva, Marcos José Da, Alonso, Alexandre Antônio & Santos, Igor Soares Dos, 2022, A new Critically Endangered species of stone breaker (Phyllanthus, Phyllanthaceae) from Central Brazil, with notes on its leaf and stem anatomy, Phytotaxa 530 (1), pp. 53-64 : 54-58

Phyllanthus pterocaulis M.J. Silva , sp. nov. ( Figs 1 , 2 )

Type:— BRAZIL. Goiás: Niquelândia, Reserva Particular de Desenvolvimento Sustentável Legado Verdes do Cerrado , Núcleo Engenho , Área do Coimbra , imediatamente após a plantação de soja, lado direito da estrada sentido Vila da Reserva, Borda de Floresta Estacional, solo argiloso, 14º33’12”S, 48º31’12”W, 569 m. a.s.l., 19 February 2021, fl., fr., M.J. Silva, I.S. Santos & B.S. Pereira 11935 (holotype UFG! , isotypes UB!, CEN!, NY!, RB!) .

Diagnosis:—This species can be differentiated from its most similar species (see table 1) by having herbaceous habit up to 13 cm tall, stem short and sparsely hispidulous, conspicuously winged in cross section, Leaves ovate with margin irregularly serrate, base truncate or cordate, hispidulous below; flowers on both sexes 5 or 6-merous, the staminate ones with three free stamens, the pistillate ones with bilobed stigma.

Description —Herbs 7–13 cm tall, annual, monoecious; stem short and sparsely hispidulous, greenish to green brownish, conspicuously winged in cross section, monopodial or simpodial, with non phyllantoid branching; lateral branches, angulate, striated longitudinally, 2–9.5 cm long, distically distributed. Cataphylls absent. Stipules 1–1.2 mm long, widely triangular, conspicuously auriculate at base, margin entire. Petiole 0.3–0.4 mm long, cylindrical, hispidulous. Leaf blade 3–6 × 2.9–3 mm, chartaceous, ovate and cordate, base truncate or slightly cordate, apex obtuse, margin irregularly serrate and ciliate by hispidulous trichomes; discolorous, opaque green and glabrous above, dark green and hispidulous below; venation brochidodromous, primary and secondary veins impressed on both surfaces. Cymules bisexual on leaf axils and base of the secondary and tertiary branches, with 1 pistillate flower and 1–3, staminate flowers; bracts widely triangular, conspicuously acuminate. Staminate flowers 0.7–0.8 mm long, pedicel 0.4–0.5 mm long, cylindrical; sepals 5 or 6, 0.3–0.32 × 0.3 mm, widely elliptic, elliptic-obovate or oblong-elliptic, apex obtuse or rounded-mucronulate; stamens 3, free, anthers horizontally dehiscent; disk with 5 or 6 obtriangular segments with rugose surface. Pistillate flowers 1.2 mm long; pedicel 0.3–0.35 mm long; sepals 5 or 6, lanceolate, oblong-obovate or oblong with a light-green or reddish central band; disk entire, patelliform; ovary 0.35–04 × 0.4 mm, globose, glabrous, styles 3, free, horizontally bilobed. Capsules 1.2–1.3 × 1.3 mm, depressed-ovate, glabrous, sepals marcescent; fruiting pedicels often bent and deflexed. Seeds 0.7–0.75 × 0.5–0.6 mm, trigonous; hilum obtriangular, terminal; testa with 9 or 10 minutely verruculose rows of arranged longitudinally along the dorsal surface, and 5 or 6 rows on lateral surfaces, light brown.

Additional specimens examined (paratype s):— BRAZIL. Goiás. Niquelândia, reserva Particular de Desenvolvimento Sustentável Legado Verdes do Cerrado, Núcleo Engenho, Área do Coimbra do lado direito da estrada sentido vila, após plantação de soja na borda de Floresta Estacional, solo argiloso, 14°33’10”S, 48°31’12”W, 576 m. a.s.l., 28 January 2021, fl., fr, M. J. Silva, B. S. Pereira, I. S. Santos & B. Gusmão 11770 ( UFG), 11771 ( UFG), 11772 ( UFG); ibd., 14°33’15”S, 48°31’11”W, 570 m. a.s.l., 19 February 2021, fl., fr, M. J. Silva, B. S. Pereira & I. S. Santos 11930 ( UFG) 11931 ( UFG), 11932 ( UFG), 11933 ( UFG), 11934 ( UFG); ibd., final da Área da Felipa, lado direito da estrada sentido Área do Zé Gordo , em borda de Floresta Estacional, 14°35’03”S, 48°24’43”W, 697 m. a.s.l., 20 February 2021, fl., fr., M. J. Silva, B. S. Pereira & I. S. Santos 11979 ( UFG) .

Distribution and habitat:— Phyllanthus pterocaulis has been collected so far in the municipality of Niquelândia, state of Goiás. Unlike many herbaceous species of Phyllanthus that grow in disturbed environments, it was found growing in shady environments at the edge of seasonally dry forests of on clay soil between 576– 750 m.a.s.l.

Phenology:—Species collected with flowers and fruits in January and February.

Preliminary conservation status:—Species with an Extent of Occurrence of 16.827 km 2, which is therefore classified as Critically Endangered (CR) Criteria B1 subcriteria b(iv, v). Also, the species forms populations with less than 50 individuals growing at the edge of dry forest currently surrounded by soybean fields, and the limits of this vegetation-type are constantly challenged by increase in plantation size.

Etymology:—The specific epithet “pterocaulis” refers to the cross section of its winged stem (“ptero” from the Greek “pterón”, plus “caulis”, from Latin).

Systematic position and morphological relationships:— Phyllanthus pterocaulis has herbaceous habit, non-phyllanthoid branching, leaves alternate and distichous, androecium with three free stamens, pistillate flowers with entire disk, ovary glabrous, fruiting pedicels often bent and deflexed, and verruculose seeds. These characters place it within Phyllanthus subg. Phyllanthus sect. Loxopodium G.L. Webster , an American group composed by six species represented by small plants that grow in damp areas or along stream beds, more rarely in dry limestone areas. These species are characterized by the distichous phyllotaxy, persistent axes with flowers on all orders of branching, pistillate flowers with entire or dissected disk, the staminate ones with three stamens free or connate and anthers dehiscing transversely; the styles are usually bifid, and seeds vary from smooth to verruculose ( Webster 1955, Bouman et al. 2018).

Considering the taxa included in P. sect. Loxopodium, the species that resemble P. pterocaulis the most are Cuban endemic P. heliotropus Whright ex Griseb. (1865: 167) and P. avicularis Müller Argoviensis (1863: 32) and P. hyssopifolioides Kunth (1817: 108) , both occurring in Brazil. All share flattened or winged branches, the staminate flowers with three stamens and segmented disk. Characters listed in Table 1 clarify the differences between these species.

According to Bouman et al. (2018) three species of Phyllanthus sect. Loxopodium occur in Brazil, one with subspecific taxa: P. avicularis , P. caroliniensis subsp. caroliniensis , P. caroliniensis subsp. guianensis ( Klotzsch, 1843: 51) G.L. Webster (1955: 46) , and P. hyssopifolioides . It is common to find unnamed or misdetermined specimens belonging to these taxa in local herbaria. Therefore, we provide a key to differentiate these and the newly described species below.

Figures

FIGURE 1. Phyllanthus pterocaulis M.J. Silva.A. Habit; B. Portion of branch, note the winged projections and hispidulous trichomes; C. Stipules; D. Leave, note the ciliate margin; E. Detail of lower side of the leaf blade showing trichomes; F. Detail of the bisexual cymules. G. Staminate flower; H. Pistillate flower in frontal view; I. Pistillate flower, note the disk and ovary; J. Fruit; K. Mericarps removed showing the carpophorous; L. Seed, lateral view; M. Seed, dorsal view. (drawings by Cristiano Gualberto, from the holotype)

FIGURE 2. Phyllanthus pterocaulis M.J. Silva.A. Habit; B. Portion of branch showing the cymules and fruit; C. Detail of the cymules; D. Staminate flower in frontal view; E. Pistillate flower in lateral view, the sepals green whitish; F. Pistillate flower in upper view, the sepals reddish; G. Fruit; H. Seeds in dorsal and lateral view. Photographs by M. J. Silva.

Tables

Table 1. Differential characters between P. pterocaulis, P. avicularis, P. heliotropus, and P. hyssopifolioides.

Characters	P. pterocaulis	P. avicularis	P. heliotropus	P. hyssopifolioides
Height (cm)	7–13	45–50	19–40	15–27
Plant sex	Monoecious	Dioecious	Monoecious	Monoecious
Leaves	3–6 × 2.9–3 mm hispidulous, ciliate at margin, chartaceous	5–15 × 3–5 mm glabrous, margin not-ciliate, chartaceous	5–12 × 2.5–6 mm, glabrous, not ciliate, coriaceous	6–12 × 2.5–5 mm, glabrous, margin not ciliate, firmly chartaceous
Stem and branches	Shortly hispidulous, winged, delicate	Glabrous, Flattened, robust	Glabrous, Angled robust	Glabrous, subcylindrical robust
Cymules	Bisexual	Bisexual	Unisexual	Unisexual
Staminate flowers	5 or 6-merous, stamens free	6-merous, stamens united	5 and 6-merous, stamens free or partially united	5-merous, stamens free
Pistillate disk	Entire, patelliform	Entire, anular	5 or 6 segmented	5 or 6 segmented
Styles	Horizontal, bilobed	Ascending, bifid	Ascending, bifid	Horizontal, bifid
Capsules diameter (mm long)	1.2–1.3	2–2.1	2.9–3	3–3.1
Seeds	Verruculose	Verruculose	Verruculose	Smooth