Lubaria Pittier has been one of many monotypic genera of the subtribe Galipeinae of the highly diverse and nearly cosmopolitan angiosperm family Rutaceae (Kubitzki et al., 2011). This family comprises about 160 genera and 2100 species (Kubitzki et al., 2011; Cole et al., 2018) of which several are of global economic importance as edible fruits (mainly Citrus), ornamentals, sources of medicinal and aromatic compounds and timber (e.g. Amyris P. Browne, Casimiroa La Llave, Chloroxylon DC., Murraya J. Koenig, Phellodendron Rupr., Ruta L. and Zanthoxylum L.) (Mabberley, 2017). Rutaceae also has a remarkable generic diversity in the Neotropics which has been confusing for many taxonomists because of the complex and continuous variability among genera and the incomplete morphological knowledge of many of them. Within the family, Kubitzki et al. (2011) recognized three subfamilies based on a combination of morphological, chemical and DNA evidence: Aurantioideae, Cneoroideae and Rutoideae. More recent molecular-only based studies have suggested either four subfamilies: Amyridoideae, Aurantioideae, Cneoroideae and Rutoideae (Morton & Telmer, 2014) or two: Cneoroideae and Rutoideae (Groppo et al., 2012; Cole et al., 2018).

Based on the description of the only previously known species, Lubaria aroensis Pittier, the genus is delimited by the combination of arboreal habit, simple opposite leaves, terminal several-branched dichasia with monochasial branches, pentamerous flowers with calyx lobes imbricate and the two outermost ones larger than the others, white zygomorphic (bilabiate) corolla with one free adaxial innermost petal (minor lip) and four connate petals (major lip), androecium of two fertile stamens flanking the minor lip and three staminodes alternating with the lobes of the major lip, filaments connate, anthers with apiculate apex and a basal appendage, and fruits with one to five follicles. At first glance, the specimens of L. aroensis could be placed in other families with simple opposite leaves and zygomorphic flowers, like Pittier (1929) reported, who initially found them misplaced in the Acanthaceae .

Lubaria is considered part of the subtribe Galipeinae (=Angostura alliance of Kubitzki et al., 2011), of which most genera are characterized by some combination of characters such as zygomorphic flowers, more or less tubular corollas, sterilization of stamens and presence of staminodes, variously modified anthers, seeds lacking endosperm and plicate cotyledons (Groppo et al., 2008; Kubitzki et al., 2011). Galipeinae is part of the subfamily Rutoideae (Kubitzki et al., 2011; Groppo et al., 2012; Cole et al., 2018) and DNA based phylogenetic studies have also suggested that it is a monophyletic group (Bruniera et al., 2015; Groppo et al., 2017; Cole et al., 2018); however, Lubaria as well as several other genera have not been yet included in a published molecular analysis of Rutaceae. Here, a new species of Lubaria from forest remnants in the middle part of the Magdalena River basin in north-central Colombia is described and illustrated, along with comments about its distribution, habitat and conservation status. In the species description, details of the leaf venation were described following the terminology of Ellis et al. (2009), the conservation status employing the IUCN Red List categories and criteria (IUCN, 2012) was established with R packpage “ConR” (Dauby, 2019; Protected Planet, 2019; R Core Team, 2019), and the distribution map was made on Arcgis 10.5.

Lubaria heterophylla Londoño-E., Ana Trujillo & Pérez Zab., sp. nov. Type: Colombia, Antioquia, Mun. Remedios: vereda Río Negrito, quebrada El Recreo, 6°53′55.04′′N, 74°29′20.07′′W, 350 m, 05 Mar 2018 [fl], Y. Londoño & J. A. Pérez 214 (holotype: MEDEL; isotypes: COL, HUA). (Figs. 1 & 2.)

Fig. 1
figure 1

Lubaria heterophylla. A. Habit and young inflorescence, zoomed view of branches surface. B. Inflorescence. C. Calyx in bud. D. Union of corolla lips. E. Flower (frontal view). F. Minor lip (abaxial and adaxial view) and the fertile stamens, zoomed view of the anthers. G. Major lip and staminodes. H. Staminode. I. Disc, style and stigma (zoomed view). J. Immature fruit with styles still present, zoomed view of the surface. (A, C from Londoño & Pérez 237; B, D–I from Londoño & Trujillo 240; J from Londoño & Trujillo 84. Drawn by Adriana Sanín E., HUA illustrator.)

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Fig. 2
figure 2

Lubaria heterophylla. A. Trifoliolate primordial leaves of which one of the three leaflets is reduced. B. Detail of leaves and branches. C. Inflorescence with senescent flowers. D. Flower, lateral view. E. Immature fruits (some with underdeveloped cocci) and senescent flowers. (A from cultivated young plant; B–C from Trujillo & Londoño 14; D from Londoño & Trujillo 240; E from Trujillo & Londoño 15. Photos by Y. Londoño, edited by Diego A. Zapata Z., HUA illustrator.)

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Diagnosis: Lubaria heterophylla differs from L. aroensis, the only other species in the genus, by its palmately trifoliolate (vs. simple) leaves of which one of the pair at a node has a shorter petiole, smaller leaf blades, and frequently only one or two leaflets, its shorter calyx (1.5–1.9 vs. 3–4 mm long), shorter corolla (9–11.5 vs. 13–16 mm long), and an apically blunt (vs. apiculate) anther connective.

Shrub or treelet up to 6 m tall, the branches villous, glabrescent, lenticellate, slightly pendulous. Leaves opposite, petiolate, usually palmately trifoliolate, but one of the pair at a node on a shorter petiole and sometimes bifoliolate or less frequently simple; petiole terete, villous, the longer at a node (11–) 30–45 (–67) × 0.6–1 mm, the shorter one (3–) 5–16 (–29) × 0.5–0.9 mm; petiolules villous, the petiolule of terminal leaflet of trifoliolate leaves (and of the longer leaflet of bifoliolate leaves) 1–10 × 0.5–0.8 mm, the petiolule of the lateral leaflets of trifoliolate leaves (and of the shorter leaflet of bifoliolate leaves) 1–6 × 0.6–0.8 mm; terminal leaflet of trifoliolate leaves 6.3–10.4 × 2.3–4 cm, blade of simple leaves 2.8–6.2 × 1.3–2.8 cm, both medially and basally symmetrical; lateral leaflets of trifoliolate leaves (2.4–) 7.8–9.2 (–12) × (0.9–) 2.5–4.2 cm, medially asymmetrical, basally with asymmetrical insertion; leaflets of bifoliolate leaves 4.1–9.2 × 1.3–3.7 cm, medially symmetrical or asymmetrical, basally symmetrical or with asymmetrical insertion; blade of leaflets elliptic, elliptic-ovate or rarely obovate, the base acute, straight or convex, when asymmetrical one side concave, the apex acute, straight or acuminate, sometimes mucronate, villous on only the primary and secondary veins adaxially, sparsely so on surface and densely so on primary and secondary veins abaxially, the margin entire, hispidulous-ciliate, glandular-punctations impressed adaxially and slightly raised abaxially; venation pinnate, simple brochidodromous; major secondaries 9–13 on each side of the midvein, (sub)equidistant, departing the midvein at ca. 60°; marginal fimbrial vein present; intersecondary veins >50% of the length of the subjacent secondary, ca. 1 per intercostal area, proximal course parallel to major secondaries, distal course reticulating or ramifying; intercostal tertiary veins irregular reticulate; epimedial tertiary veins reticulate; exterior tertiary veins looped; quaternary and quinternary vein fabric irregularly reticulate; areolation moderate; ultimate marginal venation incomplete. Inflorescence terminal, a dichasium (simple or up to twice-forked, with monochasial branches), 2.5–7 (–12.7) cm long including a peduncle 0.5–5 × 0.1 cm, bearing (3–) 13–20 (–43) flowers, the axes villous; monochasial branches 3.9–38.5 (–83.3) mm long, villous; bracts ca. 0.5 mm long, deltoid, villous; bracteoles 0.5–1 mm long, lanceolate, villous; pedicels 1–3 mm long, villous-strigose. Calyx imbricate-quincuncial in bud, the 2 outer sepals 1.5–1.9 × 1.2–1.7 mm, the 3 inner sepals 1.5–1.9 × 0.8–1.2 mm, all 5 ovate to elliptic, villosulous adaxially and villous-strigose abaxially with whitish trichomes, ciliate, sparsely to densely glandular-punctate. Corolla bilabiate, 9–11.5 mm long, white, adaxially lanuginose from 1 to 6 mm from the base and hispid to hispidulous on the rest of the surface, glandular-punctate (dark punctate when dry); the minor lip 9–11.2 × 2–3 mm, obovate, attenuated unguiculate, rounded to acute at apex; major lip 9–11.5 × 4–6 mm (width measured under the insertion of the lobes), widely obovate, 4-lobed, the lobes 2–5.2 × 1.2–3.5 mm, rounded to acute at apex; lips free from each other at base and coherent from ca. 1.5 mm to ca. 4 mm from the base, adherent to the filaments and staminodes by intertwining of trichomes on their adjacent surfaces. Androecium of 2 fertile stamens and 3 staminodes; fertile stamens flanking the minor lip, the filaments 6–6.5 × ca. 1 mm, widening up to 4 mm from the base, distally attenuate, free from each other at base and connate from ca. 1.5 mm to 4.5 mm from the base, adherent to the corolla by a lanuginous zone from 1 to 4.5 mm from the base; the staminodes 10.2–11 × ca. 1 mm, linear, densely hirsute adaxially, adherent by abaxial hirsutulous indumentum to the major lip from 1 to 5 mm from its base; anthers basifixed, 2.5–4 × ca. 1 mm (including basal appendage), obliquely oblong, laterally coherent along their adjacent margins, glabrous, occasionally with sparse trichomes, the connective eglandular, blunt at apex. Disc 1–2 mm high, cupular, inflexed, costate, shortly 5-lobed at margin, ceraceous, enclosing the ovary. Ovary of 5 free carpels with 2 ovules each, glabrous, the surface alveolate; style 6–8 mm long, curved, glabrous; stigma capitate, 5-lobed. Fruit (immature) with up to 5 dehiscent cocci, each 5 mm long, these ovate to obovate, acute at apex, glandular-punctate, rugose, glabrous, 1-seeded. Seed not seen.

Distribution and habitat.—Known from a single population of about 30 individuals growing on the bank of the lower course of a creek locally known as Quebrada El Recreo (a tributary of Río Ité), an area located in the eastern part of the municipality of Remedios, Antioquia department (Fig. 3). The climate of this area corresponds to equatorial monsoon (Am) under the Köppen-Geiger climate classification (Kottek et al., 2006) with average year-round temperatures between 24 °C and 26 °C, 2500–3000 mm of annual precipitation and a marked dry season from December to March (IDEAM, 2017). Individuals were mostly found in shaded places of the understory or below the canopy of mature trees and appeared to prefer rocky calcareous and sandy soils under the influence of supplementary humidity from the watercourse around where they grow.

Fig. 3
figure 3

Distribution of Lubaria.

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Phenology.—Flowering and fruiting in March and April.

Etymology.—Lubaria is based on the vernacular name “lúbaro” cited in the protologue of L. aroensis (Pittier, 1929), and heterophylla is derived from the Greek, “heteros-” (different) and “phúllon” (leaf), in reference to the presence of leaves with different sizes and number of leaflets on the same shoot in mature plants.

Conservation status.—Based on the apparently restricted distribution (EOO < 100 km2, AOO < 10 km2, habitat fragment < 500 km2, and the small number of individuals recorded), and the almost completely deforested landscape surrounding the riverine zone of the creek where they grow, this species should be classified as critically endangered (CR) according to the criteria B1ab(iii)+B2 of the IUCN V 3.1 (IUCN, 2012).

Taxonomic notes.—Although the two species of Lubaria share similar flowers and fruit, L. heterophylla can be distinguished from the only previously known species, L. aroensis, most readily by its leaves and corollas. In L. heterophylla, the leaves are palmately trifoliolate (rather than simple like those of L. aroensis), and one of a pair of mature leaves at a node has a shorter petiole, slightly smaller leaflets which frequently are reduced to two or one (and looking like a simple leaf). In both species, the corolla is bilabiate, with a minor lip of one petal and a major lip of four connate petals. In the new species, the major lip is tightly coherent to the minor lip (rather than free from it as in L. aroensis). The coherence occurs very near the base of the corolla by “capillinection” (Weberling, 1989: 48), i.e., the intertwining of dense pubescence on the overlapping margins of the major and minor lips. Lubaria heterophylla further differs from L. aroensis by its smaller height (shrub or tree to 6 m tall vs. tree 4–12 m tall), smaller calyx 1.5–1.9 (vs. 3–4) mm long, smaller corolla 9–11.5 (vs. 13–16) mm long, and apically blunt (vs. apiculate) anther connective.

Additional specimens examined. COLOMBIA. Antioquia: Mun. Remedios: vereda Río Negrito, quebrada El Recreo, 6°54′19.13′′N, 74°28′25.73′′W, 360 m, 1 Apr 2017 [im fr], Y. Londoño & A. M. Trujillo 80 (MEDEL); 6°54′18,06′′N, 74°28′29.40′′W, 365 m, 2 Apr 2017 [fl & fr], Y. Londoño & A. M. Trujillo 84 (MEDEL); 6°53′57.57′′N, 74°29′14.66′′W, 350 m, 5 Mar 2018 [fl], Y. Londoño & J. A. Pérez 217 (HUA, JAUM, MEDEL, SPFR); 6°54′19.84′′N, 74°28′26.69′′W, 350 m, 5 Mar 2018 [fl], Y. Londoño & J. A. Pérez 237 (COL, HUA, MEDEL); 6°54′18.65′′N, 75°31′30.78′′W, 350 m, 5 Mar 2018 [bud, fl], Y. Londoño & J. A. Pérez 238 (HUA, SPFR); 6°54′18.65′′N, 74°28′29.22′′W, 350 m, 6 Apr 2018 [fl], Y. Londoño & A. M. Trujillo 240 (COL, CUCV, FAUC, HUA, JAUM, MEDEL, SPFR); 6°53′55.04′′N, 75°30′39.93′′W, 350 m, 6 Apr 2018 [fr], Y. Londoño & A. M. Trujillo 256 (HUA, NY, SPFR); 6°54′19.84′′N, 74°28′26.69′′W, 350 m, 6 Apr 2018 [fl], A. M. Trujillo & Y. Londoño 014 (COL, CUVC, FAUC, HUA, JAUM, MEDEL, MO, NY, SPFR); 6°53′57.57′′N, 74°29′14.66′′W, 350 m, 6 Apr 2018 [fr], A. M. Trujillo & Y. Londoño 15 (COL, HUA, MEDEL).

The new species clearly belongs to Lubaria, which can be distinguished from other genera in Galipeinae by the combination of opposite leaves, a terminal several-times-branched dichasial inflorescence, calyx with two sepals slightly wider than the other three, a bilabiate corolla with a minor lip of one petal and a major lip formed by four connate petals, filaments of fertile stamens connate along adjacent margins, anthers with basal appendages and glandular punctate on the abaxial surface (but not in the connective), and ovary of free carpels that form a fruit of 1 to 5 dehiscent follicles.

The most remarkable difference between the new species and Lubaria aroensis is the presence of trifoliolate leaves but with concurrent variation of petiole length, leaflet size and leaf composition within a single individual, a condition that can be defined as heterophylly (Zotz et al., 2011). Observations of cultivated young plants showed that all primordial leaves had three leaflets but slightly unequal petioles, and generally both at a node mature as trifoliolate (Fig. 2A). However, in adult individuals in the field, the leaves with the shortest petiole at a node, were frequently either bifoliolate or simple, with smaller leaflets than the trifoliolate ones and without apparent basal abscission leaflet scars. This pattern of variation suggests that the reduction in number of leaflets could happen by a mechanism of either discretionary suppression of leaflet formation or early abortion and shedding of one or two lateral leaflets during leaf expansion. These leaf alterations eventually would cause an overall reduction in leaf area, which could result in a limitation of the amount of transpiration. The observation of mostly pairs of trifoliolate leaves in the young cultivated individuals which were watered and shaded, in contrast with more reduced leaves in individuals growing in the natural range (an area subject to an annual four-month period of elevated temperature and reduced rainfall) may suggest a connection between these post-developmental changes in the leaves and the environmental water stress in the vegetation of the area during the dry period. Consequently, the leaf structure alteration recorded in L. heterophylla could be a form of phenotypic plasticity in response to environmental conditions and then also comply with the original definition of heterophylly (Nakayama et al., 2017; Zotz et al., 2011). This leaf variation also could be alternatively explained as an architecturally related adjustment of the pair of leaves at each node to improve the sunlight exposure efficiency when the plant crown is becoming denser. Further field observations and long-term monitoring of growing individuals may help to confirm details of the leaf development and to explain this case of heterophylly.

This is the first report of Lubaria for Colombia and as suggested by the also restricted occurrences of L. aroensis, individuals of the genus seem to be limited to riparian lowland tropical forest. Lubaria heterophylla is only known from about 30 individuals in the riverine habitat of a small creek (in an area less than 10 km2) with copious calcareous rock outcrops in the north (eastern side) of the central branch of the Colombian Andes. Much of the forest in this region has been cleared, and our searches for this species in nearby forest relicts away from the river were unsuccessful. Similarly, all the collections (including the type) of L. aroensis with geographic data in the online database Tropicos.org (2019) are cited as riparian. Further studies of soil properties and other environmental variables may help to determine whether narrow microhabitat preferences can explain the disjunct and highly restricted current distribution. In addition, population biology studies and field surveys of both species are needed to assess appropriate conservation measures. In the perspective of contributing to the evolutionary knowledge in the family, further molecular phylogenetic and anatomical studies of Galipeinae including Lubaria (complementing those by Groppo et al., 2017 and El Ottra et al., 2013, 2019, respectively) would help to refine the understanding about the origin of zygomorphic flowers in Rutaceae.

Finally, with the discovery of Lubaria in Colombia, a country with a diverse geography and still many botanically unexplored areas, new records of one or both species of the genus might be found in parts of the country near the known locality of L. heterophylla in the valley of the Magdalena River and/or situated between it and those of L. aroensis in northern Venezuela (Coastal Cordillera in the states of Miranda and Falcón) and northwestern Costa Rica (provinces of Guanacaste and Alajuela). Given the relative rarity of opposite leaves and bilabiate corollas in neotropical Rutaceae, unidentified herbarium specimens of Lubaria could also remain misfiled in other families as Pittier (1929) reported.