Inflorescence and floral ontogeny in Jasminum fruticans (Oleaceae)

Abstract

The inflorescence and floral ontogeny of the oleaceous tropical bush, Jasminum fruticans L. were studied using epi-illumination light microscopy and compared with other Oleaceae. The flowers are arranged in a thyrsoid inflorescence with a determinate pattern of development. Deviations from the common pathway of floral ontogeny in Oleaceae observed in J. fruticans are characterised by pentamery in calyx and corolla, diagonal position of sepals, some deviation from acropetal and simultaneous initiation of floral organs. Sepals are helically initiated, beginning with the abaxial sepal. Formation of petal lobes from the ring meristem also is not simultaneous with the initiation of three petals before the others. Concurrently with the formation of corolla ring, two stamens are initiated sequentially. Two median carpels are the last organs to be initiated. Unusual features of organ enlargement include the quincuncial-imbricate aestivation of the corolla and formation of trichomes on the distal portion of petals and stamens.

A developmental basis for stochasticity in floral organ numbers

“…The floral organ numbers are determined during the initiation and fate determination of the floral organs. Scanning electron microscopic studies of the initiations of floral organs revealed that the sepal primordia initiate in sequential, helical order in the Ranunculaceae (Ren et al, 2010 ), the main target of the present paper, and in several other families such as the Caryophyllaceae (Lyndon, 1978 ) and the Oleaceae (Dadpour et al, 2011 ). These species exhibit considerable variation in floral organ numbers, as we will show.…”

“…arbor-tristis , whereas J . fruticans shows pentamerous helical initiation but stochastically develops four or six sepals (Sehr and Weber, 2009 ; Dadpour et al, 2011 ). Thus, there are three patterns of Oleaceae sepal initiation: the simultaneous initiation of four sepals, the extra two sepals (4 + 2) found in N .…”

“…Many Ranunculaceae species such as Ranunculus exhibit semi-whorled arrangements (Figure 3C ; sometimes referred as false-whorls or pseudo-whorls) in their flowers (Schöffel, 1932 ). Even in some whorled flowers, the primordia initiation is sequential; in other words, their positional arrangement is transiently semi-whorled [e.g., Caryophyllaceae (Lyndon, 1978 ) and Oleaceae (Dadpour et al, 2011 )]. In the Caryophyllaceae species Silene coeli-rosa , the positions of the primordia were measured quantitatively in the early stage of floral development, showing that the sepals took on a semi-whorled arrangement (Lyndon, 1978 ).…”

“…Because we assumed semi-concentric arrangement, there are several situations that the ERF model is unlikely to account for. Many of the Oleaceae species, except for Jasminum (Dadpour et al, 2011 ), show simultaneous initiation of all organs within a whorl, or even ring-like (early sympetalous) development of a whorl (Sehr and Weber, 2009 ). In such cases, the variation in the radial positions of the organs within a whorl should be negligibly small, differing from the assumption of the ERF model.…”

Seed morphology and seed coat anatomy of Fraxinus, Ligustrum and Syringa (Oleeae: Oleaceae) and its systematic implications

“…In the past the variation in seed morphology has been used variously in plant systematics ranging from identification (Sako et al 2001, Khalik andVan der Maesen 2002) and taxonomic circumscription (Constantinidis et al 2001, Mendum et al 2001, Amini et al 2011, Sadeghian et al 2014, Ghimire et al 2015a, 2016a, Arabi et al 2017) to phylogenetic inference (Hufford 1997, Arambarri 2000 and character-state evolution (Fukuhara 1999, Simons andHedin 1999). Although quite a few embryological, floral, and carpological studies of Oleaceae have been carried out (Rohwer 1993, 1994, Sher and Weber 2009, Dadpour et al 2011, Naghiloo et al 2013, Ghimire and Heo 2014, Ghimire et al 2015b, studies on comparative seed morphology and seed coat anatomy are still scarce for the family. Therefore, it is necessary to undertake an extensive investigation of the seed morphology and anatomy of the Oleaceae to evaluate their applicability to the tribal and subtribal taxonomy.…”