Mollinedia leucantha M.Molz & D.Silveira, 2021

Molz, Martin & Silveira, Denise, 2021, A new endemic species of Mollinedia (Mollinedieae, Monimiaceae) from the southern limit of the Atlantic coastal moist forest, Phytotaxa 508 (3), pp. 279-288 : 283-286

Mollinedia leucantha M.Molz & D.Silveira , sp. nov. ( Fig. 1 )

Type: — BRAZIL. Rio Grande do Sul: Três Cachoeiras, in a lowland forest fragment beside RS-494 State Road , 20 m elev., -29.440303, -49.917633 (datum WGS84), November 4, 2013, D. Silveira, F. Gonzatti & L. Machado 86 (holotype ICN 176705 !, isotypes RB ! HAS !). ( Figs. 2A–G and 3A–B ).

Diagnosis: —This species is morphologically similar to Mollinedia schottiana ( Sprengel 1827: 407) Perkins (1900: 677) , particularly to the form described under the synonym Mollinedia floribunda by Tulasne (1855: 41), with which it shares leaf shape, pubescent flowers and appearance of the fruitlets, but differs in the light-brown color of the lower surface of the leaves (versus gray-green to yellowish-brown in M. schottiana ), appressed, short and densely matted trichomes (vs. erect in the branches and appressed in the leaves, longer and less entangled), and light-grey flowers with a finely granular surface (vs. darkened flowers with a smoother surface).

Description: —Dioecious treelet, evergreen, 3–10 m tall, up to 13.5 cm DBH and often with more than one trunk (2–6), frequently arched; rhytidome slightly fissured, occasionally detaching in fine scales. Young stems and leaves yellowish green to lime green, covered by light-yellow-tomentose trichomes (white-tomentose in new buds). Branches densely ramified, cylindrical, arched and glabrescent, with 2–8 cataphylls at the base of new growth, imbricate, deciduous, leaving little gnarled scars in old branches, deltoid to suborbicular, keeled, upper surface sparsely pubescent but the keel densely light yellow-tomentose, lower surface light yellow-tomentulose. Leaves opposite, lamina fresh green on the upper surface and lime-green to grayish-green on the lower surface, drying pale green to brownish on the upper surface and grayish-brown on the lower surface, chartaceous, elliptic, lanceolate, oblanceolate or obovate, 6.1–12.8(–14.5) × 1.8–4.8(–5.4) cm, base cuneate or rarely attenuate, apex broadly acute to acuminate, ending in a monimioid tooth; petioles 0.2–1.2 cm, glabrescent, cylindrical and canaliculate; blade entire or more often sparsely serrate, with 2–12 pairs of short monimioid teeth mostly in the distal half, glabrous on the upper surface (except for a few trichomes on the midvein) and ivory- to yellowish-tomentose on the lower surface, white-tomentose in fresh material, leaf margins sometimes thickened, often slightly revolute; venation brochidodromous, veins inconspicuous on the upper surface, except for the midvein (apparent but flattened), and prominent on the lower surface, the midvein protruding, secondary veins 5–7 pairs, diminishing toward the margin and anastomosing 2–6 mm from it, tertiary venation only slightly visible. Inflorescences opposite pairs of 3-flowered (rarely 5-flowered) botryoids or uniflorous (reduced to a single flower), bearing two bracteoles on the external side of the lateral flowers or on both sides of the single flower; inflorescences arising from the axils of cataphylls immediately below the terminal bud; cataphylls scale-like, deciduous, ovate, keeled. Staminate flowers at anthesis 6.5–9.5 mm diam., receptacle hemispherical, tepals 4, tepal lobes fused at the base and free at the apex, triangular; white- to ivory-tomentose, trichomes emerging from a finely granular surface; bracteoles 1 at the base of the external portion of the pedicel on each of the lateral flowers (even in 5-flowered), linear, early deciduous; stamens 19–20, sessile, anthers hippocrepiform, confluent at the apex. Pistillate flowers at anthesis 13–16.5 mm diam., receptacle turbinate (somewhat flattened), tepals 4, tepal lobes fused at the base and free at the apex, deltoid; white- to ivory-tomentose, trichomes emerging from a finely granular surface; bracteoles 2 at the base of the pedicel, linear, early deciduous; carpels 22–34. Fruiting receptacle head-like, 0.9–1.6 cm in diam. (dried), at the base markedly concave, slightly roughened at the surface of the concavity, when fresh greenishyellow, external surface often covered by white trichomes. Peduncle 0.9–1.4 cm long, enlarged, more thickened at the extremes. Drupelets 17–34, oblong, ellipsoid, broadly ellipsoid or obovoid, with a short tip (remnant of the style), sessile, regularly spaced so that they hardly touch each other, white-farinose on the surface.

At first glance, differences between M. leucantha and M. schottiana are not readily noticeable. Mollinedia schottiana has great variability in its characters (e.g. Vattimo 1957, Lírio & Peixoto 2017), hence it is easily confused with other species. Figure 2 shows differences between the two side by side in nature, while Table 1 presents the main distinctive characters. Besides morphological differences, the two species differ in the distribution, which is much broader in M. schottiana , ranging from the Brazilian state of Bahia (≈ 15º S) to Rio Grande do Sul (30º41’ S) ( Lírio et al. 2020), growing in coastal moist forests and inland seasonal forests, while M. leucantha is restricted to lowland coastal moist forests of the southern Brazilian states of Santa Catarina and Rio Grande do Sul.

Mollinedia leucantha was recognized as an entity separate from M. schottiana by Reitz (1961), who mistakenly assigned the specimens to M. calodonta Perkins (1900: 678–679) . Four decades later Peixoto et al. (2001) described and illustrated the same entity as M. calodonta , in which the distal quarter of the leaf blade is deeply serrate, and staminate flowers have 36–38 stamens, whereas the blade of M. leucantha is entire or more often sparsely serrate, with shallow teeth, and the staminate flowers have only half the number of stamens. We examined several specimens identified as M. calodonta from Santa Catarina and most of them were M. leucantha . Along the herbaria work we noticed that M. leucantha was also confused with M. blumenaviana Perkins (1900: 669–670) , M. chrysolaena Perkins (1902: 744) , and M. eugeniifolia Perkins (1900: 661) . Mollinedia blumenaviana features distinctive narrowly lanceolate leaves and 16–17 stamens, so that it hardly can be mistaken for any other species in southern Brazil. Mollinedia eugeniifolia has obovate or elliptical leaves strongly revolute at the margin and few stamens (12); it is known only from the type and like M. blumenaviana does not resemble any other species. Since it was never collected again, even in the forest inventory recently conducted in the state of Santa Catarina (including the type locality), we suppose that it is probably extinct. Specimens collected in the state of Rio Grande do Sul and identified as M. chrysolaena (ICN 7862, ICN 32439, and ICN 34947) were all M. leucantha , which has white-tomentose trichomes in contrast to golden-yellow trichomes in M. chrysolaena . Other specimens were also mistaken for M. calodonta , but the type of this species (Mendonça, F.R., 212, n.d.; holotype, B, probably destroyed; Berlin Negative No. 13417 of holotype at Field Museum) is from Rio de Janeiro and quite different in regard to appearance as well as to Perkins’ description.

Scanning electronic microscopy (SEM) of flowers: — Figure 3 shows the most remarkable differences between the flowers of M. leucantha , with a granular-papillose surface, often with few more or less straight trichomes, and M. schottiana , with a surface so densely covered by trichomes that only minute patches of the surface between the hairs are visible. At moderate magnification, the granular-papillose surface of M. leucantha flowers appears to be covered with extremely shriveled trichomes, which to our knowledge is a unique feature among the species of the genus occurring in southern Brazil. However, it is important to note that the flowers of some specimens may present the surface densely covered with short trichomes.

Distribution maps: — Brazil, restricted to the Atlantic coastal moist forest (dense ombrophilous forest) in the Brazilian states of Santa Catarina and Rio Grande do Sul ( Fig. 4 ). Due to the proximity to Santa Catarina, it is possible that M. leucantha also occurs in Paraná State, but so far we have not seen material from that state.

Conservation status assessment: —Habitat loss and fragmentation constitute the main threats. The extent of occurrence was calculated at 14,506 km 2, by which M. leucantha falls under the category of VU (vulnerable), B1ab(i,ii,iii). Without the use of digital elevation models the EOO would be 27,207.98 km 2, then falling into the category NT (Near Threatened). We noticed that, despite being abundant in some areas, the species has not been found in several fragments visited, even within suitable habitat. Further studies are necessary to estimate number of individuals in different populations.

Mollinedia leucantha occurs in one of the most severely fragmented regions in southern Brazil, intensely modified for more than 200 years, as noted by Saint-Hilaire (1887) in his “Voyage à Rio Grande do Sul ” between 1821 and 1822. The lowland forests in the coastal plain of southern Brazil are being severely depleted. Urban expansion and conversion to pasture and agricultural areas have been the main causes of forest reduction. Additionally , the clearing of understory vegetation to house cattle is a serious problem affecting shrub and treelet species populations, as well as the natural regeneration of canopy trees. This was the case at the type locality where the new species was collected, where all shrubs and treelets (including all individuals of M. leucantha ) were cut.

These problems have led to a decline in the extent of occurrence, area of occupancy and quality of habitat, which pose challenges not only for the conservation of one, but for many endangered species of plants and animals. Since most known populations occur in lowland forests (usually up to 100 m elev.), conservation actions must necessarily pass through the development of a lowland forests conservation plan.

Phenology: —The sprouting of the inflorescences occurs between August and September and the anthesis between October and November. In contrast, the flowering of M. schottiana , the most similar species, follows about 20 days later. Staminate flower anthesis precedes that of the pistillate flowers by a few days. The development of the young fruits begins shortly after anthesis, often even before shedding of the calyptra. Fruits were found mature between April and June.

Etymology: —The specific epithet refers to the white color of the flowers in nature, present even in the buds.

Habitat and distribution: — Mollinedia leucantha is an understory treelet endemic to the Atlantic coastal moist forest in southern Brazil, where it grows in old secondary to old-growth lowland and submontane forests. It can be relatively abundant, usually with an aggregated distribution pattern. It belongs to a group of Atlantic species restricted to a narrow elevational belt, ranging from well-drained lowland areas to submontane forests up to 350(–500) m elev. On the other hand, M. schottiana occurs from swampy to well-drained lowland areas up to 900 m elev., and penetrates widely into inland semi-deciduous forests.

Vernacular names and uses: —Pimenteira, capixim. There are no known uses for this species.

Additional specimens examined: — BRAZIL. Rio Grande do Sul: Dom Pedro de Alcântara, 10 October 2012, D. Silveira & B.O. Boeni 09 ( ICN) ; Morrinhos do Sul, Pixirica , 30 April 2013, D. Silveira, M. Molz & B.O. Boeni 43 ( ICN) ; Osório, Morro da Borrússia , 13 July 1994, S.N. Davi s.n. ( ICN 114992 ) ; Torres, Perdida , 30 October 1992, J.A. Jarenkow 2176 ( PEL) ; Torres, mato do Sr. Felisberto , 1-2 October 1976, L.R.M. Baptista s.n. ( ICN 34947 ) ; Três Cachoeiras, fragmento na beira da ERS-494 , 25 June 2012, M. Molz s.n. ( ICN 174477 ) ; Santa Catarina: Florianópolis, Morro do Ribeirão , 15 October 1968, Klein & Bresolin 7875 ( ICN) ; Florianópolis, Rio Vermelho , 17 October 1968, R.M. Klein 7940 ( P); Florianópolis , Tapera / Ribeirão , 18 November 1969, Klein & Bresolin 8435 ( ICN) ; Garopaba, 20 August 2007, R. Hentschel s.n. ( ICN 157971 ) ; Governador Celso Ramos, Jordão , 18 October 1971, Klein & Bresolin 9769 ( ICN) ; Ibirama, Horto florestal I.N.P. , 15 May 1956, R.M. Klein 1985 ( K) ; Itajaí, Morro da Fazenda , 3 November 1955, R.M. Klein 1747 ( G) ; Laguna, 19 October 1929, F.C. Hoehne s.n. ( HAS 73470 ) ; Lauro Muller, Vargem Grande , 19 September 1958, Reitz & Klein 7236 ( K) ; Luiz Alves, Braço Joaquim , 30 September 1954, Reitz & Klein 2131 ( M) ; Rio do Sul, 13 September 1959, Reitz & Klein 7151 ( M) ; São João do Sul, 6 September 1977, K. Hagelund s.n. ( HAS 88180 ) ; Sombrio, Pirão Frio , 31 October 1959, Reitz & Klein 9300 ( L) .

Figures

FIGURE 1. Holotype of Mollinedia leucantha.

FIGURE 2. Mollinedia leucantha (A-G). A. Branch. B. Rhytidome. C. Leaf adaxial surface. D. Leaf abaxial surface. E. Pistillate flowers. F. Staminate flowers. G. Fruits with drupelets. Mollinedia schottiana (H–N). H. Branch. I. Rhytidome. J. Leaf adaxial surface. K. Leaf abaxial surface. L. Pistillate flowers. M. Staminate flowers. N. Fruit with drupelets.

FIGURE 3. Scanning electronic microscopy (SEM) of flowers of Mollinedia leucantha (A–B) and Mollinedia schottiana (C–D). A. Flower detail and tepals. B. Appearance of the granular-papillose surface covered by few trichomes. C. Flower surface densely covered by trichomes. D. Detail of the trichomes.

FIGURE 4. Distribution of Mollinedia leucantha in the Brazilian states of Rio Grande do Sul and Santa Catarina, corresponding to the southern limit of the Atlantic coastal moist forest.