Synopsis of the spurred species of Lobelia section Stenotium (Campanulaceae) in Sierra Madre Occidental, Mexico, and the description of two new species

Abstract

The genus Lobelia is cosmopolitan and comprises 423 species in 18 sections. Lobelia sect. Stenotium is the most diverse group with 153 species, has a wide distribution in continental North America and is segregated into two subgroups based on the presence of spurred flowers. There are 16 spurred Lobelia species that occur in streamside or seep areas, throughout pine and oak mixed forests from USA to Costa Rica, but they are frequent along the Pacific slopes of the Sierra Madre Occidental (SMO), Mexico, where 10 species grow. In this paper we present a synopsis of the spurred species of Lobelia in the SMO and propose two new taxa. First, Lobelia rzedowskii is morphologically similar to L. ayersiae, L. cordifolia and L. endlichii but differs by its rosulate leaves, blades 0.5–1.5 × 0.4–1 cm, subsessile, racemose to paniculate inflorescences, with (4–)10–35(–191) flowers, flowers 4–6 mm long including hypanthium, spur 0.5–1 × 0.5–0.8 mm, with the lower two calyx lobes positioned at the middle portion of the spur, white corolla with a yellow spot above lobe sinuses on the throat and staminal tube 1.3–2.5 mm long. Second, Lobelia saturnini is morphologically similar to L. knoblochii, L. macrocentron, L. mcvaughii and L. villaregalis, but differs from them by leaves (2–)4–14(–17) mm long, petioles 2–6(–17) mm long, solitary flowers, flowers 12–16 mm long including hypanthium, hypanthium 1.2–2.5 mm long, spur 2–3 mm long, pedicels (1.3–)2–9(–12) cm long and anthers 1–2.2 mm long. We include an identification key for spurred species of Lobelia in the SMO, photographs, distribution notes with a map, and illustrations.