Cytinaceae A. Rich.

Genera Included: Bdallophytum Eichler and Cytinus L.

The relationship between Bdallophytum and Cytinus has been recognized since the time of Solms-Laubach (1894) who placed them both in the same tribe Cytineae of Rafflesiaceae. Molecular evidence supports their affinity but showed they were not closely related to Rafflesiaceae but were part of Malvales (Nickrent et al. 2004), specifically allied with Muntingiaceae (Nickrent 2007).

Habit: Achlorophyllous, holoparasitic herbs. True roots lacking. Leaves reduced to scales.

Parasitism: Root parasites on a variety of shrubs and trees. Cytinus hypocistis of the Mediterranean region is found on members of Cistaceae. As a genus, Cytinus is rather nonspecific, parasitizing plants in a number of families. Bdallophytum, endemic to the neotropics, is parasitic on the roots of Bursera (Burseraceae) as well as other genera such as Gyrocarpus, Haematoxylum, Cochlospermum, Ficus, and Guazuma (Alvarado-Cardenas (2009). Infection likely starts in the roots and ramification within the host results in flowering shoots being produced some distance from the main stem.

Roots: The endophyte filamentous or plate-like, resembling a fungal mycelium inside the host tissues. For the anatomy of the endophyte, the following description is borrowed from Forstmeier et al. (Beitr. Biol. Pflanzen 58:299-311, 1983):

"The haustorial structure of Cytinus hypocistis (Rafflesiaceae) was investigated. After penetration of the cortex and cambium of the host root, the parasite pierces deeply into the central cylinder. Parasitic cells with meristematic activity intrude below the cambium layer of the host detaching it from the xylem. Dividing cells form small complexes of parasitic tissue which spread as well in direction of the longitudinal root axis as also by enveloping the central cylinder between cambium and xylem. At last, a closed cylinder of the parasite is formed. This cylinder consists of a cambium and two surrounding layers of tissue: an inner medullary and an outer cortical plate. The cambium of the host which was detached from the xylem by the parasitic cells temporar(il)y suspends its activity. Later on, it becomes active again, depositing new layers of xylem on the parasitic tissue. Within the xylem rays, however, the parasitic tissue penetrates these host layers and continues to separate the host cambium from the host xylem. A multiple repetition of this process results in several alternating layers of xylematic parasitic and host tissue."

Stem: Absent

Leaves: Scale-like, imbricate around the base of the flower and along the inflorescence axis.

Inflorescence: Flowers borne singly or in clusters at apex of inflorescence axis. Terminal spikes bear few to several flowers, often crowded at the terminus in an umbellate pattern. Flowers subtended by (usually) two bracteoles.

Plant Sex: Flowers bisexual or (more commonly) unisexual.  For Cytinus, some species are monoecious (e.g. C. hypocistis, C. ruber) whereas others are dioecious (C. capensis, C. glandulosus, C. sanguineus, C. visseri). In Bdallophytum, B. americanum and B. andrieuxii are dioecious whereas B. oxylepis is gyno-monoecious (Alvarado-Cardenas (2009).  Visser (1981) reports that male and female plants of Cytinus invade separate host individuals.

Staminate Flowers:
Calyx: Perianth (sometimes called tepals or a perigone) tubular, composed of four to nine imbricately arranged lobes. Usually brightly colored (red, yellow, pink, purple).
Corolla: Absent.
Nectary: In South African Cytinus, cavities formed between the perianth lobes contain nectaries. As stated in Visser (1981) "Many papillose protuberances are present around the edges of these cavities that may contain up to about 300 microliters of viscous sweet nectar."
Androecium: the 8 (to 20?) stamens are connate, united into a column (monadelphous). The anthers are united into a ring at the apex of the column, some with spurs (from the connective) that project beyond. The anther sacs appear folded and open extrorsely by longitudinal slits to release the pollen.
Pollen: Ca. 38 um, spherical, multiaperturate (C. dioicus, C. sanguineus), diporate in C. ruber [see photos courtesy of A. Takhtajan in Cronquist, 1981 and Visser 1981]. Cytinus (subg. Hypolepis) pollen occurs in tetrads whereas in Bdallophytum pollen is in monads.

Carpellate Flowers:
Calyx: Perianth tubular, lobes smaller than in staminate flowers (S. African species).
Corolla: Absent.
Nectary: as above.
Androecium: absent.
Gynoecium: Epigynous; with a columnar style terminated by a globose or capitate, viscous stigma. Ovary unilocular with 8-14 deeply intrusive, discrete parietal placentae.
Ovule: Numerous, 180 to 220 um long, orthotropous, with tenuinucellate nucellus without parietal cells. As stated in Bouman and Meijer (1994):

"Nucellar epidermis, about 7 cells in circumference, and does not form a nucellar cap. Inner integument is dermal in origin and initially two-layered, overgrowing the nucellus and forming a distinct micropylar canal. The inner integument later becomes three-layered by periclinal divisions of its inner layer. Cells of the outer layer enlrge and count about 11 cells in circumference. The outer integument is arrested in its development, dermal in intiation, two layered, and forms an irregular rim at the ovular base. The outer integument contributes to the formation of the mucilage."

Pollination: Visser (1981) states relates that other botanists have implied sunbirds pollinate Cytinus owing to the brighly-colored perianth. In contrast, his observations strongly implicate ants as the pollinating agents of the S. African species.  Flies pollinate the New World Bdallophytum.

Fruit: For Cytinus, an indehiscent or irregularly dehiscent fleshy berry. The sweet, white, viscid and/or slimy pulp surrounds numerous small seeds.

Seed: Numerous and tiny, ranging in length from 0.2 to 0.5 mm. The urceolate seeds are embedded in the placental tissue during fruit development. The outer integument contributes to the mucilaginous nature of the fruit pulp. Outer seed coat (testa, exotegmen) is sclerotic, one cell layer thick. Tegmic cells are irregular to polygonal in shape with pitted walls (Bouman and Meijer 1994). As stated by Bouman and Meijer (1994): "Although the seeds of Bdallophytum and Cytinus have the same basic orthotropous structure, they show distinct differences in testal pattern, in the absence or presence of the rudimentary outer integument, and in structural details."

Embryo sac Development: Polygonum type (Bouman and Meijer 1994).
Embryo: Mature embryo ten or more cells in length; with an irregular cellular arrangement
Endosperm: development nuclear; thin-walled, containing oil and protein bodies.

Chromosomes: n=16 for Cytinus hypocistis

Link to Family Description in Delta

SIUC / College of Science / Parasitic Plant Connection / Cytinaceae / Description
Last updated: 19-Sept-12 / dln