A developmental model for the corolla in Rubiaceae. Cryptic character states in corollas of the Spermacoceae alliance
Methods – Floral developmental studies using scanning electron microscopy (SEM) and light microscopy (LM).
Results – In Spermacoce, the tubular corolla with epipetalous stamens originates from an annular primordium. In Sacosperma and Pentas, the tubular corolla develops similarly with the stamens fixed basally. In Paederia and Pentodon, individual petal primordia originate on a ring wall. Next, stamen primordia appear adaxially on the ring wall. Then, the bases of the petals fuse partially, resulting in fenestrated tubular corollas. In Sacosperma and Pentas, corolla splits are actively formed in an initially closed tubular corolla.
Conclusions – The tubular corollas of the species studied in Spermacoce, Sacosperma and Pentas are early sympetalous. Those in Paederia and Pentodon are late sympetalous. The tubular corolla results from a combination of three developmental processes: the formation of (1) a stamen-corolla tube, (2) a corolla tube sensu stricto, and (3) postgenital fusion of petals. The final form of the tubular corolla and the stamen insertion depend on the relative activity of these processes. Consequently, similar looking tubular corollas may constitute different character states. The corolla splits studied constitute two different cryptic character states in respectively Sacosperma/Pentas and Paederia/Pentodon.
Keywords: (CRYPTIC) CHARACTER STATES; ANNULAR INTERCALARY MERISTEM; COROLLA SPLITS; COROLLA TUBE SENSU STRICTO; FENESTRATED COROLLA; FLORAL DEVELOPMENT; POSTGENITAL FUSION; RUBIACEAE; SEM; STAMEN-COROLLA TUBE
Document Type: Regular Paper
Publication date: July 1, 2015
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