of Parasitic Flowering Plants
For a number of parasitic flowering plants, their closest
have been known for some time. These include Cassytha
Lauraceae, Lennoaceae with Boraginaceae, Orobanchaceae with
in the traditional sense, and Cuscuta with
For others, particularly the holoparasites Hydnoraceae,
and Rafflesiaceae, placement among photosynthetic angiosperms
has been difficult. For this reason, their traditional classifications
Through DNA sequencing and molecular phylogenetic analyses,
relationships between parasitic and nonparasitic angiosperms have
been greatly clarified. The topology of the phylogenetic tree
shown below is from APG2 (2003) and is derived from the large-scale
molecular phylogenetic analysis of angiosperms by Soltis et al.
(2000). Parasitic plant families that were not included in that
analysis were added (e.g. Mitrastemonaceae, Rafflesiaceae, etc.)
based on more recent evidence (see below). Groups enclosed by
a dashed border represent hemiparasites, that is, plants that
obtain water and nutrients from a host yet still produce their
own carbohydrates via photosynthesis. Groups enclosed by a black
border are holoparasites that do not photosynthesize (or do so
at very low levels), hence must obtain carbohydrates from their
host plants. Two groups, Orobanchaceae and Convolvulaceae (Cuscuta)
contain both hemi- and holoparasites. Overall, it appears that
parasitism has arisen independently in angiosperms 12 times
(red taxon names on tree).
To navigate to a specific
click the name in the colored box.
Notes on the various
the sole parasitic member of the large family Lauraceae, is
assigned to this family based on morphological and molecular data.
Its superficial resemblance to Cuscuta is
an excellent example of convergent evolution.
were used to place Hydnoraceae with Aristolochiaceae s. lat. (Nickrent
et al. 2002). The exact topology of the component families of
this order (Aristolochiaceae, Hydnoraceae, Lactoridaceae, Piperaceae
and Saururaceae). More recent analyses (Nickrent
2005, IBC abstract) suggests Hydnoraceae is most closely
The analyses conducted
by Soltis et al. (2000) resolved the sandalwood order as monophyletic,
but this clade was part of a large polytomy among the core eudicots.
The number of taxa involved in this polytomy is quite high, involving
caryophyllids, rosids and asterids. Recent molecular using complete
chloroplast genomes from over 80 angiosperms (Moore et al. 2008)
indicates that Santalales is sister to Caryophyllales and asterids.
previously placed in its own order (Balanophorales, Takhtajan
1997), has been shown from molecular evidence (Nickrent
et al. 2005)
to be related to Santalales. This result is
but supported by both nuclear and mitochondrial genes from the 2005
analysis and a more recent study by Su and Hu (2008) using floral
B-class homeotic genes. The exact
relationship between Balanophoraceae and Santalales remains to be
classified with Balanophoraceae, the family Cynomoriaceae has
been shown to be a component of Saxifragales. See Nickrent
et al. (2005) for a complete discussion of this finding.
The APG2 classification
considered Krameriaceae as an acceptable, monophyletic alternative
to Zygophyllaceae. This "family" is unresolved at the
base of the eurosid I clade.
considered here in the strict sense (including Rafflesia,
Rhizanthes, and Sapria, i.e.,
clade") was placed with Malpighiales by Barkman et al. (2004)
using mitochondrial matR gene sequences. This position was confirmed
et al. (2004) using both nuclear SSU rDNA as well as
sequence data. More recent evidence (Davis et al. 2007) places Rafflesiaceae within Euphorbiaceae.
clade" is composed of Cytinus and Bdallophyton.
Mitochondrial matR and nuclear SSU rDNA both strongly support
a position for this family in Malvales. See Nickrent
et al. (2004).
clade" is composed of Apodanthes, Berlinianche, and
Pilostyles. Mitochondrial matR and nuclear SSU rDNA
indicate either a relationship with Malvales or Cucurbitales (Nickrent
al. 2004). Additional sequencing and analysis indicate this
family is part of Cucurbitales (Nickrent, unpublished).
with but a single genus Mitrastema, was shown to be
to Ericales by Barkman et al. (2004) using mitochondrial matR
gene sequences. This result is confirmed using nuclear SSU rDNA
and mitochondrial sequence data (Nickrent
et al. 2004).
have traditionally been placed in their own family, but APG2 lumps
"Lennoaceae" with Boraginaceae, a family with which
they are clearly related as shown by both morphological and molecular
evidence. Boraginaceae s. lat. is currently unresolved at the
base of the euasterid I clade.
name formerly referred only to an assemblage of holoparasitic
taxa that were recognized to be related to the hemiparasites of
Scrophulariaceae. More recent circumscriptions of this group (see
Young et al. 1999, Olmstead et al. 2001) place all parasitic "scrophs"
in a monophyletic family Orobanchaceae. Morphological and molecular
evidence clearly place this family in Lamiales.
parasitic genus of Convolvulaceae is Cuscuta that
been placed in its own family, Cuscutaceae. Analysis of sequence
data from four chloroplast gene regions resulted in Cuscuta
being nested within Convolvulaceae (Stefanovic and Olmstead 2000),
thus the classification of APG2 is supported.
SIUC / College of Science /
Connection / Relationships: Flowering
Last updated: 08-Oct-08 / dln