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Telopea Vol. 6(4): 1996 
continue to consider the relationships of Onagraceae as additional information on the 
embryology of other families of Myrtales becomes available. 
Relationships within Onagraceae: A comparison among the genera of Onagraceae 
indicates that the foUowing four embryological features differ significantly within the 
family. (1) Anther wall development is predominantly either the Basic or the 
Monocotyledonous type; (2) the ovule archesporium is one- or multi-celled; (3) the inner 
integument is retarded in development or not; and (4) the parietal tissue lying above the 
tetrad of megaspores is either thin or thick. The distribution of features of these four 
characters within Onagraceae is presented in Table 5, along with that of features o 
integumentary histogenesis (Tobe & Raven 1985) and of divided microsporangium 
(Tobe & Raven 1986a), features that we found earlier to differ within the family. 
Ludxuhia is the only genus that characteristically has a one-celled ovule archesporium, 
in contrast to the multi-celled archesporium in all other genera. Ludivigm now appears 
unambiguously to be a sister group to the remainder of the 
basis of evidence from floral morphology and anatomy (Hyde 1981; Hoch ej al. 1993) 
and from molecular analyses of both ribosomal DNA (Bult & Zimmer 1993) and 
chloroplast rbcL data (Conti, Fischbach & Sytsma 1993). For example, Ludioigia has 
floral nectaries on the gynoecium, instead of at the gynoecium and floral tube |unction 
as in all other genera, and both central and transseptal bundles for ovule supply, 
instead of only transseptal bundles as in all other genera (Hyde 1981). The difference 
in the number of archesporial ceUs in an ovule supports the hypothesis that Uidivigm 
does indeed represent an evolutionary branch separate from the rest of the family. 
Hauya (Hauyeae) and all genera of the tribe Onagreae except Gaijaphijtum agree with 
one another in having markedly thick parietal tissue in the ovule. Hainja further agrees 
with Calylophiis, Gaiira, and Glarkia of Onagreae in having the Monocotyledonous type 
anther wall formation, instead of the Basic type common to all other genera 
Coincidences between Hauya and members of Onagreae have already been indicated 
by other embryological evidence. For instance, Hauya shares with Galylophus and Gaura 
a distinctive histology of the outer integument (Tobe & Raven 1985), and also shares 
with Galylophus, Gaum and Glarkia the apparent apomorphy of microsporogenous 
tissue divided by septa composed of parenchyma and tapetum into many small packets 
(Tobe & Raven 1986a). Tliis evidence, thus, suggests a close relationship oi Hauya with 
tribe Onagreae, particularly with Galylophus and Gaura, and probably also with Glarkia. 
However, several molecular analyses using both nuclear (Crisci et al. 1990; Bult & 
Zimmer 1993) and chloroplast DNA (Sytsma, Smith & Hoch 1991; Conti, Fischbach & 
Sytsma 1993), contradict this placement of Hauya near Onagreae, instead supporting a 
close relationship of Hauya to Fuchsia and Circaca. Ongoing molecular analyses that 
include all relevant taxa and 'total-evidence' analysis of the studies already available 
mav resolve this controversy, and provide a robust hypothesis within which to interpret 
the evolution of these embryological characters. The chalazal seed wing shared by 
both Hauya and Xylouagra seems to represent a parallel (homoplasious) evolution, 
since no other evidence supports a close relationship between them. 
In Gayophytum, unlike other members of the tribe Onagreae, but like Epilobium (tribe 
Epilobieae), the early development of the inner integument is retarded. In addition, 
Gayophytum resembles Epilobium, rather than other Onagreae, in having thin parietal 
tissue in the ovule. This rather surprising suggested relationship appears to be 
supported by sequence data from analysis of the internal transcribed spacer region 
(ITS) of the nuclear ribosomal gene (Baum & Sytsma, unpublished data). This suggests 
that Onagreae may not be monophyletic because Epilobieae appears to be nested 
within it; the two tribes together, however, appear to form a monophyletic group. 
