Carpel initiation

Hibbertia often in fascicles sometimes temporal overlap with carpel initiation ... 

Fabales (Leguminosae) Pisum sativum, Swartzia spp. Pisum carpel initiated Sattler, 1972b after first (abaxial) Tucker, 2003 stamen primordia. Prenner, 2003, Centrifugal stamens in 2004a, b some Swartzia spp. Carpel before stamens in some Papilionoideae ... 

Malvales Bixaceae, Cistaceae, Cochlospermaceae, Malvaceae s.l. Many polyandrous genera Mostly intrazonal centrifugal stamens often in fascicles sometimes temporal overlap with carpel initiation Corner, 1946 Van Heel, 1966 Tucker, 1999 [Pavonia-Malvaceae)... 

Fig 11.7 A. celastrifolia, carpel initiation. The organ-free floral apex is marked with an asterisk in aU. Note that in all samples the carpellary cleft (if already present) is pointing towards the floral centre. (A) Three very similar carpels suggesting simultaneous initiation. (B) Four carpels initiated and very similar in size. (C)-(E). Five carpels formed in no defined sequence. (F) Six carpels formed apparently in anticlockwise sequence. (G) Six carpels formed in no discernlhle sequence (i.e. erratic). (H) Seven carpels formed, six are of similar developmental stage, one lags behind. Scale hars = 100 pm in all. 

The discovery that in A. celastrifolia carpel initiation starts before the last stamens are formed, confirms Endress (1994, p. 103) observation that early carpel initiation is a characteristic of species in which stamens are formed on a ringlike androecial mound. However, early carpel formation is also frequently found in Papilionoideae with only ten stamens in two whorls (e.g. Daviesia cordata, Prenner, 2004d) and in Caesalpinioideae (c.f. Prenner and Klitgaard, 2008). 

It is intriguing that early developmental stages in A. celastrifolia closely resemble the distantly related Nelumbo (Nelumbonaceae) (Hayes et al., 2000). In particular, the clear-cut border between androecial ring-wall and central floral meristem on which the carpels will be formed is striking. In contrast, in polyandrous and multicarpellate Ranunculaceae carpel initiation commences more or less gradually... 

Bailey, I. W. and Swamy, B. G. L. (1951). The condupUcate carpel of dicotyledons and its initial trends of specialization. American Journal of Botany, 38, 373-379. 

Triuridaceae (Pandanales) Centrifugal carpels in fascicles central stamens initiated first in Lacandonia Rudall, 2008... 

Fig 9.2 Development of sepals, petals and carpels in Conostegia. (A), (E) C. icosandra (B) C. xalapensis (C) C. pittieri (D), (F) C. macrantha (G) C. rhodopetala (H) C. centronioides. (A) Young inflorescence with older apical flower and two lateral flowers with hracteoles. (B) Partial view of inflorescence with apical flower showing early petal initiation and lateral flower with sepal initiation. (C) Early initiation of gynoecial dome... 

Fig 9.5 Flower morphology of Heterocentron elegans (A)-(B), Clidemia octona (C)-(F) and of Dissotis rotundifolia (G)-(ff). (A) Mature flower bud with four petals (removed) and eight stamens. (B) Detail of flower showing a style surrounded by an extension of the ovary wall at the base. The anthers are provided with basal auriculate appendages. (C) Development of sepal lobes surrounding petal primordia. (D) Initiation of stamens and carpels. Note the... 

E) Older floral hud with massive androecial ring-wall (circle) distinctly separated from inner part of the flower. (F) Side view of androecial ring-wall. Arrows show the direction of stamen initiation. In the centre of the flower four carpel primordia are just formed (c). 

Van Heel (1983) studied the ontogeny of free carpels from a wide range of distantly related plants. For Amherstia nobilis (Caesalpinioideae) he showed abnormal gynoecia with a second smaller carpel formed in an adaxial position. One sample (his Fig 117) shows the early initiation of such an aberrant carpel situated at the proximal end of the adaxial cleft (i.e. it resembles part of the well-formed carpel rather than an entirely independent organ see also van Heel, 1993). Besides these abnormalities, there are no well-documented instances of regularly multi-carpellate flowers in Caesalpinioideae. Sattler (1973) documented one anomalous flower of the mimosoid Albizia lophanta with two young carpels with their sutures facing each other. While in Albizia this pattern must be seen as aberrant, there are other mimosoid taxa that show more than one carpel as a stable character in all flowers. 

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