Anatomia comparada das inflorescências de Parianinae (Poaceae: Bambusoideae: Olyreae)

Abstract

Parianinae is a monophyletic subtribe among the three herbaceous bamboo lineages of the tribe Olyreae (Poaceae, Bambusoideae). It contains about 45 species circumscribed in three genera, Parianella (2), Pariana (27), and Eremitis (16). The subtribe can be recognized by gynecandrous, clusters of staminate spikelets surrounding a single pistillate spikelet. The origin of the gynecandrous is unknown, and the uniqueness of the reproductive structures to the other Olyreae, added to the glumes in the staminate spikelets of Parianinae, make its interpretation more complex. Furthermore, Parianinae inflorescence remains poorly known, and an anatomical study can improve the knowledge about Olyreae and Parianinae relationships. The four species in the study were collected and fixed in FAA 50 for 48 hours and preserved in 50% ethanol. The inflorescences were dissected, dehydrated, and embedded in histological resin to produce serial crossection 6 to 10 µm thick. Slides were stained with toluidine blue and mounted using synthetic resin. The images were organized and illustrated in graphics editing software, including some 3D reconstruction. The inflorescences of Parianinae are composed (synflorescences) and mainly constituted by gynecandrous. Taquara also has synflorescences, but spikelets are arranged in secondary axes. The gynecandrous base has spikelets fused with the inflorescence primary axis, showing by vascularization. On the other hand, Taquara does not show a fusion of parts of the inflorescence. Parianinae staminate spikelets have two lateral laminar structures with two to three vascular bundles. The staminate anthecium possesses lemma, palea, three lodicules, and the androecium with a variable number of stamens, except Eremitis, where the lodicules are absent. All structures have a wide variation in the number of vascular bundles. Pistillate spikelets possess two glumes, lemma, palea, three lodicules, a variable number of staminodes, and the bicarpellate gynoecium. Eremitis have no lodicules and staminodes. All structures have a wide variation in the number of vascular bundles. Our results showed that the inflorescences of Parianinae are alternate, rarely whorled, as well as in Taquara. Based on the morphological pattern of the Olyreae inflorescences, two events that added up over time may have conferred the origin of the Parianinae gynecandrous. In general, the staminate spikelets of all species have similar morphology, except for the glumes present only in Parianinae and the variation in the number of stamens. Pistillate spikelets also have similar morphology, but in Taquara, they are pediceled and inserted individually on the secondary axes.