GENERIC RELATIONSHIPS

Syngonium is typical of the subfamily Colocasioideae, whose members have in common articulated laticiferous tubes and leaves almost always having reticulated veins, with the secondary lateral veins joining into a collective vein between the primary lateral veins. In addition, all that have been studied in the field have milky sap.

Schott (1856) in Synopsis Aroidearum classified only the diclinous genera of Araceae. He separated these genera into Efilamentatae and Filamentatae, the latter containing only the genus Stylochiton. Efilamentatae was divided into two parts, Stenozeugmaticae and Pachyzeugmaticae, the latter divided into Gyminogoneae (pistillate flowers lacking staminodia) and Peristatogoneae (pistillate flowers with staminodia). Gyminogoneae was divided into 2 tribes, Caladiinae and Philodendrinae. Caladiinae contained 5 subtribes with genera as follows:

The subtribes of Caladiinae were later reduced by Schott (1858) as follows:

Hutchinson (1932) arranged the family Araceae into 18 tribes and mistakenly over-emphasized the scandent habit of Syngonium in placing it with Philodendron in the subfamily Philodendroideae, which contains neither articulated laticiferous tubes nor milky sap and also lacks the reticulate-veined leaves of the subfamily Colocasioideae.

In the most recent complete revision of the subfamily Colocasioideae by Engler & Krause (1920) three tribes were included. The two smaller tribes were the Syngonieae with 2 neotropical genera, Syngonium and Porphyrospatha Engler and the Ariopsideae with the single Himalayan genus Ariopsis Nimmo. The third tribe Colocasieae with 5 subtribes contain 12 genera. The Subtribe Steudnerinae with 12 species contains the genera Steudnera C. Koch, Remusatia Schott, and Gonotanthus Klotzsch. The Subtribe Hapalininae contains only the genus Hapaline Schott with 5 species, and the Subtribe Colocasinae contains only Colocasia Schott with 8 species. These first three subtribes are almost exclusively Asian in distribution. The Subtribe Caladiinae with Caladiopsis Engler, Caladium Vent., Aphyllarum S. Moore, Chlorospatha Engler, and Xanthosoma Schott is exclusively neotropical and contains about 65 species. The Subtribe Alocasiinae contains 2 genera, Alocasia Schott with 70 species in the Old World and Schizocasia Schott with 4 species in the Philippines, Indochina, and Australia.

The Ariopsideae is distinguished from the Colocasiinae and the Syngonieae by having the synandria of the staminate inflorescence united. The Colocasiinae is distinguished by unilocular ovaries with placentation basal, parietal or subcentral, whereas the Syngonieae has ovaries bilocular (or unilocular by abortion), the ovules being 1 or 2 per locule and anatropous. Syngonieae is also the only tribe in the subfamily with scandent plants.

Because of their neotropical distribution and similarly veined leaves, as well as the frequent presence of milky sap, certain members of the Caladiinae, namely Caladium and Xanthosoma, have been confused with Syngonium. Caladiinae is terrestrial, either acaulescent with subterranean stems or caulescent with short, usually erect stems, whereas Syngonium is always epiphytic, frequently with scandent stems.