Zamia oligodonta

Zamia oligodonta is a species of cycad in the family Zamiaceae, endemic to the Department Of Risaralda in the Western Cordillera of Colombia. It was described as a new species in 2003 by Eduardo Calderón-Sáenz and Dennis W. Stevenson. The species is distinguished from all other members of the genus Zamia by the combination of elliptic leaflets with heavy veins that produce undulating plicate leaflets, thick sub-apical teeth on the leaflets, a acuminate or caudate leaflet apex, and no more than three leaves on the stem crown. It is part of the Wallisii subclade within Zamia, which also includes the closely related Z. wallisii and Z. montana.

Taxonomy

Zamia oligodonta was first described by Eduardo Calderón-Sáenz and Dennis W. Stevenson in 2003. The description was based on cultivated plants originally collected in Risaralda, Colombia, held by Calderón-Sáenz (holotype: Calderón-Sáenz 174). The specific epithet oligodonta derives from the Greek roots oligo (few) and odonto (teeth), referring to the small number of teeth present in the apical region of each leaflet.

In 2009, Anders J. Lindstrom synonymized Z. oligodonta under Z. montana, arguing that the characters used to distinguish the two — chiefly the subterranean stem and differences in leaflet morphology — reflected ontogenetic variation within a single species rather than genuine taxonomic difference. This synonymy was accepted for several years and reflected in major checklists of the time.

However, a 2015 taxonomic revision by Calonje, Morales, López-Gallego, and Roldán — based on new fieldwork in wild populations in both Risaralda and Antioquia — provided evidence that Z. oligodonta and Z. montana are morphologically distinct and geographically separated species. The revision re-established Z. oligodonta as a valid species. The original description was noted to have been based on cultivated plants, which attained smaller dimensions than wild individuals; in situ observations confirmed that wild plants are substantially larger than the cultivated specimens on which the species was first described.

Molecular phylogenetic studies, including a time-calibrated species-tree analysis of the genus Zamia published in 2019, confirmed that Z. oligodonta and Z. wallisii form a well-supported clade — the Wallisii subclade — within the broader South America Zamia lineage. Both species share a suite of characters including subterranean stems, prominently veined and extremely broad coriaceous leaflets, and ovoid female cones with relatively few but large seeds, and both occur on the western flank of Colombia's Western Cordillera. Z. montana, which also bears prominently veined leaflets and occurs in the same geographic region, was suggested to belong to this subclade as well, though it was not sampled in the 2019 study.

Description

Zamia oligodonta is a small to medium-sized cycad with a typically subterranean stem, up to 40 centimetres long and 11 centimetres in diameter, bearing triangular cataphylls. Wild adult plants can produce up to three leaves, with leaf petioles reaching approximately 2.7 metres in length, substantially larger than the cultivated individuals on which the original description was based. The petiole base bears sparse prickles.

Leaflets are narrowly elliptic to elliptic in shape, and bear prominently raised veins on their upper surface so that they appear to be undulating or plicate — a character they share with the related Z. wallisii and Z. montana. The leavelets have a acuminate to caudate apex and thick, prominent teeth confined to the sub-apical region of the leaflet margin, giving the species its name. The number of teeth is low relative to other Zamia species with toothed leaflets.

Like all species of Zamia, Z. oligodonta is dioecious, with individual plants producing either pollen cones (microstrobili) or seed-bearing cones (macrostrobili). There are one to three pollen strobili on a stem apex. Pollen strobili are ovoid-cylindrical and seven to 11 centimetres long and 2.0 to 2.7 centimetres in diameter. Pollen strobili emerge yellow-green in color, turning yellow-biege as they mature. There is one ovulate strobilus on a stem apex. Ovulate strobili are ellipsoid, erect, and 17 centimetres tall and 11 centimetres in diameter. Ovulate strobili emerge reddish-brown in color, turning brown and light tan at maturity. Seeds are ovoid pyramidal in shape, 3.5–4.2 centimetres long by 2.2–2.8 centimetres wide. Immature seeds are pink, turning orange with maturity. Pollinating agents have not been observed for Z. oligodonta, but many other species of Zamia are known to be pollinated by beetles of the Pharaxonotha and Rhopalotria genera.

Both male and female strobili have been observed in September and October on plants under cultivation. Ovulate strobili at various stages of development have been observed in wild populations, confirming that reproduction is ongoing in the field. Strobili develope on wild plants in the spring, with pollination probably occurring in April and May and seeds maturing in October.

Distribution and habitat

Zamia oligodonta is endemic to the department of Risaralda in western Colombia, where it grows in premontane rainforest on the Pacific slope of the Western Cordillera at elevations of 1,500 to 1,800 metres above sea level. This places it among the highest-elevation neotropical cycads, though it occurs at somewhat lower elevations than its relative Z. montana, which ranges from 1,750 to 2,080 metres in the neighbouring department of Antioquia. The two species are geographically separated by approximately 160 linear kilometres.

At least five subpopulations are known, one of which occurs within a protected area in Risaralda. The region where the species is native retains a considerable amount of forest cover, and recruitment appears healthy across all known populations, with individuals of different ages — including seedlings, juveniles, and adults — observed in the field. Fertile seed strobili at different stages of maturity have been recorded in at least two populations, indicating that [...] reproduction is ongoing.

Specific locality information has been deliberately withheld from published accounts of the species in order to reduce the risk of illegal collection.

Conservation

Zamia oligodonta was initially listed as Data Deficient in the Red List of Colombian cycads due to lack of field data at the time of that assessment. Following field surveys carried out in support of the 2015 taxonomic revision, Calonje et al. recommended that the species be reclassified as Endangered under IUCN Criteria B1ab(i–v)+2ab(i–v); C1, based on a total extent of occurrence estimated at approximately 30 km², an area of occupancy estimated at approximately 5 km², and evidence of ongoing habitat decline. The total adult population was estimated at around 1,000 individuals across the five known subpopulations.

The IUCN Red List subsequently assessed Z. oligodonta as Critically Endangered. The principal threat to the species is habitat destruction, particularly deforestation for the conversion of forest to cattle pastures and agricultural land. Deforested areas of otherwise suitable habitat confirm that the species is in decline across parts of its range.