Systematics of the Cyclanthaceae, especially Sphaeradenia and Chorigyne
Harling (1954a) described the genus Sphaeradenia to accommodate eight species segregated from Carludovica, of which C. angustifolia (=S. angustifolia) was the first to be described (Ruiz & Pavón 1798). He recognized 41 species in Sphaeradenia, of which 35 were described by himself (1950, 1954a, 1958, 1963, 1972, 1973). Since then, Grayum & Hammel (1982), Galeano & Bernal (1984), and Hammel (1986a) have described three additional species. During the last decades, the need for a thorough taxonomic treatment of this genus has become evident.
In my revision of Sphaeradenia (Eriksson 1995), I recognize 53 species and subspecies, of which 21 were described as new. Most of the earlier described ones are quite differently circumscribed, compared to previous views. The generic circumscription is essentially similar to the one by Harling (1958), although I have found it necessary to transfer two species to Chorigyne (Eriksson 1989), and make some emendations.
The variation found within taxa is not only between individuals or populations,
but also to a large extent within individuals (Erikssson 1995), and especially
the following should be taken into consideration in this context: (1) The
variation in leaf blade size and division within taxa is partly serial,
and highly correlated, such that leaves produced by young plants, or lower
down on the stem, are shorter and more bifid than those produced by older
plants or towards the stem apex. (2) During the development from anthesis
to mature fruit, which takes several months, the spadix generally undergoes
drastic morphological changes in most structures. The differences may be
considerable also between young and mature infructescences, the states in
which most individuals are found.
Sphaeradenia is supported as the monophyletic sister-group to Stelestylis and Chorigyne (Eriksson 1994b). It is characterized by, e. g, one apical placenta, a unique feature in the Cyclanthaceae (Eriksson 1994b, 1995). Character states shared with the two latter genera are, e. g., anthers with secretion globule and a seed coat with enlarged cells. The presence of secretion globules is polymorphic in Sphaeradenia, but this is obviously due to later reversals within Sphaeradenia. Other reversals found in a few species are probably, e. g., the vine-like habit and the occurrence of thin leaf blades. Furthermore, some species lack adaxial perianth lobes of the staminate flowers, a synapomorphy supporting the Stelestylis-Chorigyne clade that has certainly evolved independently within Sphaeradenia.
The phylogeny within Sphaeradenia could not be satisfactorily resolved using a cladistic approach, due to excessive homoplasy. I have therefore sketched a rough evolutionary scenario in the genus (Eriksson 1995), as judged from an outgroup comparison with Stelestylis, where the species are assigned to the following informal groups: the Sphaeradenia laucheana group (species 1-15), the S. steyermarkii group (16-32), the S. pachystigma group (33-37), the S. cuatrecasana group (38-39), the S. garciae group (40-43), and the S. acutitepala group (44-50). Some of the species in the S. laucheana group possess many ancestral features, and this group is possibly paraphyletic, whereas the other groups to various extent are characterized by rather many supposedly derived traits. Derived features in Sphaeradenia are, e. g., the following: long internodes; leaf blades that are very small or very large, or have closely seated ridges; anthers without or with very large secretion globule; spadix with few fruits; fruiting tepals that are connate, apically cleft, or have distinct staminodial protuberance or dorsal swelling; fruiting stigmas that are uncinate, widely separated, wing-like, surpass the tepals in height, or have proximal projections; curved seeds.
Sphaeradenia has an Andean-centred distribution, ranging from southern Nicaragua to western Bolivia, and extending into Venezuela and adjacent Brazil (Eriksson 1995). The species are commonly found in humid to wet areas from sea-level up to c. 2500-3000 m altitude, or occasionally higher up. While most species occur in lowland rain forest, montane rain forest, and cloud forest, or secondary habitats adjacent to these, a few taxa prefer more marginal habitats, such as mangrove, very steep cliffs, and white sand areas. Habitat-sympatric species of Sphaeradenia are often met with.
I have subdivided the distribution range of Sphaeradenia into nine phytogeographical areas, based on correlated species distributions and area endemism. These areas conform in large scale with the ones proposed by others (e. g. Gentry 1982), with the following notable exceptions: the Huancabamba deflection, usually considered a strong barrier (e. g. Simpson 1975), has not had a marked influence on the distributions, and, furthermore, the species of Sphaeradenia are generally not distributed across the Andes. Taxa occurring in mountainous areas and in the Amazonian lowlands (areas A-H) often have restricted distributions, whereas those found in the Pacific lowlands (I), and to some extent also the Cordillera Oriental (B), are more widespread. Many closely related taxa have vicarious distributions, geographically or altitudinally separated, except those found in the coastal areas, which are largely sympatric.
The main centre of diversity is on the western slopes of the Cordillera
Occidental, and in the Pacific lowlands, in Colombia and adjacent Ecuador
(part of areas A and I), an area in which Sphaeradenia was probably
not initially differentiated (Eriksson 1995). A comparison with the proposed
phylogeny of Sphaeradenia suggests that the centre of origin, where
most species of the S. laucheana group are distributed (B, C, F-H),
is found in the eastern parts of the present range of the genus. The species
of the S. steyermarkii, S. pachystigma, S. cuatrecasana,
and S. garciae groups, with rather many derived traits, are centred
in the Cordillera Occidental and the mountainous areas in Central America
(A, D, E), and the species of the S. acutitepala group, exhibiting
many derived features, occur in the Pacific and Atlantic lowlands (I). From
the area where Sphaeradenia originally diversified, the genus probably
spread and differentiated in the northwestern Andes, followed by the mountains
of southern Central America, and, most recently, the wet, coastal lowlands
of northwestern South America and Central America. This phytogeographical
analysis further suggests that colonization of Central America has taken
place repeatedly. Major diversifications in the genus are probably rather
recent (Pliocene), and have been associated with the uplift of the Andes,
the formation of a substantial land mass across the Isthmus of Panama, and
the emergence of the coastal plains.
Maintained by Roger Eriksson and last updated August 17, 2006.