Rustia

  • Authority

    Delprete, Piero G. 1999. Rondeletieae (Rubiaceae). Part I. Fl. Neotrop. Monogr. 77: 1-226. (Published by NYBG Press)

  • Family

    Rubiaceae

  • Scientific Name

    Rustia

  • Type

    Type species. Rustia formosa (Chamisso & Schlechtendal ex de Candolle) Klotzsch.

  • Synonyms

    Henlea, Stomandra, Rustia formosa (Cham. & Schltdl.) Klotzsch, Henlea thibaudioides H.Karst., Rustia thibaudioides (H.Karst.) Delprete, Stomandra costaricensis Standl.

  • Description

    Genus Description - Shrubs to trees, sometimes with small buttresses; bark grayish-pale brown, smooth. Stipules interpetiolar, below petiole attachments, free at base, entire, narrowly triangular, readily caducous. Leaves petiolate, lanceolate, elliptic to ovate, usually acuminate at apex, pellucid-punctate; petioles thickened at base, rarely pulvinate; domatia absent or a tuft of sparse hairs. Inflorescences terminal, solitary, paniculate, racemoid secundiflorous or thyrsoid secundiflorous; lateral branches (when present) opposite, decussate, usually monochasial. Flowers protandrous; hypanthium narrowly obconical, turbinate to cupulate. Calyx cupular or extremely reduced, with barely visible lobes or truncate, persistent. Corolla tubular, cupular to campanulate, with more or less spreading lobes, thin to fleshy, white, red, green, or yellow-green; tube short to long tubular, glabrous to puberulent inside; lobes (4-)5 (-6), deltoid to narrowly triangular; aestivation valvate to valvate-reduplicate with contact zone. Stamens (4-)5, partially or completely exserted, attached near the base of the corolla tube; anthers dorsifixed near the base, opening by 2 apical pores. Pollen tricolporate, exine reticulate to foveolate (sometimes minutely echinate). Style exserted; style branches short, thick, ovate to oblong. Ovary 2-celled, obconical to turbinate; placentation axile; ovules many n each locule, horizontally inserted; immature fruits green to red, carnose. Capsules coriaceous to woody, globular, turbinate, or obovate; dehiscing loculicidally; disk septicidal dehiscence present in old capsules of some species. Seeds small, pointed at the ends, angular or with minute marginal wings.

  • Discussion

    Taxonomic History

    The type species of Rustia was first presented by Chamisso and Schlechtendal (1829) as Exostema formosum but without description, therefore as nomen nudum (for detailed information about the nomenclature of this species see Rustia formosa). De Candolle (1830) validated Exostema formosum Cham. & Schltdl. ex DC., as part of Exostemma sect. Pseudostemma; after a brief description, he stated, "Species Brasilianae. An Genus proprium?" Under sect. Pseudostemma he included is. cuspidatum St.-Hil. [= Bathysa cuspidata (St.-Hil.) J. D. Hook.], E. australe St.-Hil. [= Bathysa autralis (St.-Hil.) J. D. Hook], E. formosum [= Rustia formosa], and E. souzanum Martius ex DC. [Bathysa sp.?].

    Rustia was founded by Johann Friedrich Klotzsch (1846), who dedicated its name to Dr. Rust ("Dem Andeken des verbosteren Präsidenten Dr. Rust gewidmet"). Under the genus Rustia Klotzsch (1846) placed three species: R. formosa, R. sellowiana (validated by direct reference to Exostemma formosum var. leprosum Cham. & Schltdl.), and R. pohliana (which he described).

    Karsten (1859) established the genus Henlea with H. thibaudioides, later adding (Karsten, 1861) //. splendens [= R. thibaudioides]. Henlea has been treated as a dubious taxon (Robbrecht, 1988, 1993). In the present treatment all the species of Henlea have been treated as synonymous with either Ladenbergia or Rustia. Henlea thibaudioides (the type species of the genus) is here transferred to Rustia, and Henlea is treated as synonymous with Rustia (see discussion under R. thibaudioides, and rejected species below).

    Baillon (1880: 471-472) included both Tresanthera and Henlea in Rustia, stating that Rustia has "poricidal or shortly rimose [anthers], enclosed or exserted" and that it is closely related to Condaminea.

    Hemsley (1881) transferred Exostemma (sect. Pseudostemma) occidentale Benth. to Rustia (see discussion under R. occidentalis) without comment.

    Schumann (1889) described three additional Rustia species (R. secundiflora [= R. thibaudioides], R. angustifolia, and/?, gracilis) from South America, and synonymized R. pohliana and R. sellowiana under R. formosa. He correctly included Henlea under Rustia but erroneously transferred Henlea rosea [= Ladenbergia muzonensis (Goudot) Standi.] to Rustia (Schumann, 1891).

    Urban (1931) described Rustia haitiensis from specimens without flowers and with old capsules without seeds. This species remains dubious because only sterile material was available, and it almost certainly does not belong to Rustia (see doubtful species).

    Standley (1930a) transferred Henlea splendens to Rustia, apparently without noticing the obvious similarity to R. secundiflora [= R. thibaudioides] and to H. thibaudioides [= R. thibaudioides]. He also maintained R. rosea [= Ladenbergia muzonensis (Goudot) Standi.; see excluded species] and described R. ferruginea [= Bathysa sp.] (Standley, 1916),/?. isernii [=Alibertia isernii] (Standley, 1940), R. longifolia [= Dolichodelphys chlorocrater] (Standley, 1930b) and R. venezuelensis (Standley & Steyermark, 1953).

    Standley (1947) established the genus Stomandra [= Rustia] which he described as different from Rustia in having smaller flowers and corolla tube shorter than the lobes. Both of these characters are not sufficient to separate the two genera, and Lorence (in Burger & Taylor, 1993) recently transferred S. costaricensis to Rustia.

    Donald Simpson (1976) published a short revision of the Rustia species occurring in western South America, and validated Standley’s unpublished R. rubra. In addition, he correctly transferred R. isernii to Alibertia, erroneously treated R. longifolia [= Dolichodelphys chlorocrater] as synonymous with Tresanthera condamineoides, and declared that the short description of Henlea thibaudioides [= R. thibaudioides] "is insufficient to permit any taxonomic decision on its status" and that "it may be something other than Rustia."

    Dwyer (1980) described Rustia panamensis [= R. costaricensis (Standi.) Lorence], without noticing its close resemblance to Stomandra costaricensis.

    Discussion: Rustia is unique in the Rubiaceae in having poricidal anthers opening by two distinct apical pores. The closely related Tresanthera also has anthers pointed at apex, but its dehiscence is by one lateral triangular pore (below the apex); it also has larger fruits, and flattened and truncate seeds. Both Rustia and Tresanthera are also unique in the Rubiaceae in having leaves with "pellucid glands." These two genera are in turn closely related to Condaminea, with which they share filaments attached at base of corolla tube and multiseeded loculicidal capsules with minute seeds horizontally inserted. Condaminea differs from Rustia and Tresanthera in having four foliose stipules per node (vs. two per node), anthers that open by longitudinal slits, deciduous calyx, sessile to subpetiolate leaves, and leaf blades without pellucid glands (as in the vast majority of Rubiaceae). The flowers of Rustia consistently have valvate aestivation (sometimes valvate-reduplicate), are protandrous (the stigma is receptive only after the anthers are dried up), and vary considerably in size, shape, and habit. In R. occidentalis, R. dressleri, and R. bilsana the flowers are fleshy and usually erect, with anthers convex toward the center and closely united, and buzz-pollinated by bees. In R. thibaudioides, R. rubra, R. viridiflora, and R. schunkeana the flowers are non-fleshy, pendulous, brightly colored (red-green), with anthers included or partially exserted (consistent within the species), and commonly visited by hummingbirds, butterflies, and bees. In R. alba, R. formosa, R. simpsonii, and R. gracilis the flowers are non-fleshy (thin), white, either erect or nodding, with anthers exserted well beyond the corolla, and commonly visited by bees. None of the species has been reported to have flowers with any particular fragrance, except for R. formosa and R. alba (pers. obs.).The seeds of Rustia are minute, horizontally inserted, non-winged, and irregularly shaped, varying from apically truncate to uncinate, and 3-4-sided. Rustia is encountered as small shrubs, tall shrubs, to medium-size trees. At least one species (R. alba, pers, obs.) has been found with small buttresses. The wood is usually soft and of no particular use, and the bark is usually smooth to rugose, and pale brown to grayish.Rustia has 14 species, ranging from Nicaragua to southern coastal Brazil. The center of diversity of Rustia is in South America. Ecuador has the largest number of species (six), three of which are endemic. Four other species are endemic to southern Brazil, mostly in the states of São Paulo and Rio de Janeiro.