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Revision of Spathacanthus Characteristics Thomas F. Daniel Department of Botany California Academy of Sciences Golden Gate Park San Francisco, CA 94118

Main Characteristics Phylogenetic Analysis Generic Description & Key to Species S. hahnianus Additional Specimens Examined S. hoffmannii Additional Specimens Examined S. parviflorus Additional Specimens Examined Acknowledgments & Literature Cited Figure Legend: Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

The generic affinities of Spathacanthus have never been adequately addressed. Lindau (1895) placed the genus in the tribe Asystasieae which he characterized as having "Rahmenpollen" (i.e., 3-colporate and 6-pseudocolpate pollen with the pseudocolpi in each mesocolpium fused near the poles to form pseudocolpal ellipses), four stamens usually with dithecous anthers, and two seeds per capsule valve. Bremekamp (1965) included Lindau's Asystasieae within subfamily Ruellioideae, tribe Justicieae, subtribe Odontoneminae. Examination of pollen in Spathacanthus (S. hahnianus: Breedlove & Smith 21618, Hernández G. 1777, Hernández G. & González L. 1855, Wendt et al. 2769; S. hoffmannii: Liesner et al. 15444, Skutch 3325; S. parviflorus: Matuda 1696, Ramírez-Marcial & Quintana-Ascencio 507, Skutch 961, Steyermark 46632) reveals grains that are similar to most others in Bremakamp’s (1965) Odontoneminae. They are usually 3-colporate and 6-pseudocolpate (Fig. 1). The two pseudocolpi in each mesocolpium are sometimes fused near one or both poles, but with equal frequency they are not. Similar variation in fusion of pseudocolpi is commonly encountered among American genera of Odontoneminae (Daniel 1998). However, two features of pollen in Spathacanthus are noteworthy. Unlike most American Odontoneminae, the interapertural surfaces of the exine (excluding the pseudocolpi) are not conspicuously reticulate. Rather, they vary from being foveolate to fossulate to verrucate to rugulate. The absence of a conspicuously reticulate exine is treated as a derived character in Spathacanthus relative to other American Odontoneminae. Secondly, variation in aperture number was noted in S. parviflorus (Fig. 1g--i). Pollen of Skutch 961 and Steyermark 46632 has four colpi and eight pseudocolpi; pollen of Matuda 1696 consists of grains with four colpi and eight pseudocolpi together with grains having three colpi and six pseudocolpi; and pollen of Ramírez-Marcial & Quintana-Ascencio 507 (although consisting of poorly formed grains) has pollen with three colpi and six pseudocolpi. Among Mexican Acanthaceae, variation of aperture number within a species has been encountered only in Stenandrium dulce (Daniel 1998). Even variation of aperture number within a genus is uncommon among American Odontoneminae; it has been noted only in Odontonema (Daniel 1995b). Additional sampling of pollen in Spathacanthus is clearly warranted. The presence of four stamens is not common among Bremekamp's Odontoneminae. The only other American genus with four dithecous stamens in this subtribe is Chalarothyrsus Lindau. Chalarothyrsus is a unispecific genus occurring in the dry forests of western Mexico. Pollen of Chalarothyrsus resembles that of Spathacanthus in sometimes having pseudocolpal ellipses in the mesocolpia; however, it resembles that of most other American Odontoneminae by having a reticulate exine. These two genera can be distinguished by the following couplet: Perennial herbs or small shrubs to 1.5 m tall; calyx small (to 5 mm long), 5-lobed, the lobes homomorphic; corolla red, 13--16 mm long; capsule 12--18 mm long; seeds permanently retained in capsule and partially fused to inner capsule wall ........................................................ Chalarothyrsus. Large shrubs or small trees to 8 m tall; calyx large (15--40 mm long), 2-parted, the 2 segments entire or variously lobed at apex; corolla white to yellow, 23--95 mm long; capsule 40--85 mm long; seeds expelled from mature capsule, not fused to inner capsule wall............... Spathacanthus.