Hosts: A wide variety of mainly woody hosts, including plants of agricultural and economic value as well as indigenous and endemic species.  Among the important economic hosts are fruit plants such as citrus (Citrus sp.), mango (Mangífera indica), cloves (Eugenia aromatica), nutmeg (Myristica fragrans), and avocado (Persea americana). It also is frequently found on many other endemic tropical species worldwide.  In Hawaii, it commonly occurs on native or naturalized woody coastal hosts such as Tournefortia argentea (tree heliotrope), Scaevola sericea (beach naupaka), Metrosideros polymorpha ('ohia lehua), Morinda citrifolia (noni), Pandanus sp. (screw pine) and on their surrounding plants, including a wide variety of shrubs and herbaceous succulents, weeds, grasses and groundcovers in Hawaii.  According to Nickrent (2002), C. filiformis "appears to be totally indiscriminate in host choice, often covering and parasitizing dozens of host species simultaneously."

Pathogen (scientific name): Cassytha filiformis L.  Photo above: C. filiformis on 'ohia lehua (M. polymorpha) growing on the South Kona coast of the island of Hawaii (Photo: S. Nelson, UH-CTAHR).

Synonymy: Cassytha senegalensis A.Chev.; Cassytha guineensis Schumach. & Thonn.

Pathogen common names: dodder laurel; love vine; woe vine; kauna'oa pehu, kauna'oa malo-lo, kauna'oa uka, kauna'oa, malolo, pololo (Hawaiian language). 

Type of pathogen: phanerogam (seed plant). 

Genus information (Cassytha): A genus of about 20 species, most in Australia, a few in South Africa, and one pantropical species (C. filiformis). The genus name derives from kesatha, Aramaic for "a tangled wisp of hair."  Cassytha species are parasitic vines with small haustoria (an infectious, adhesive structure used to withdraw nutrients from host organs through host cell membranes); stems are filiform, containing chlorophyll. Leaves are reduced to minute scales.  Flowers are sessile or pedicellate, in heads or spicate or racemose inflorescences; floral tubes are shallow, enveloping the fruit; tepals number 6, the outer 3 smaller than inner 3, persistent; fertile stamens 9, those of the third whorl with 2 basal glands, the fourth whorl reduced to staminodia; anthers are dithecal.  The fruit is enclosed in the floral tube with a persistent perianth.

Plant family: Lauracea

Description of Cassytha filiformis: Stems are green to orange, filiform, and glabrous.  Leaves are reduced to minute scales, ca. 1 mm long, easiest seen near tips of stems.  Flowers are sessile & few in spicate inflorescences 1(-2) cm long, each one subtended by an ovate bract and 2 ovate bracteoles, those with ciliolate tips; tepals are glabrous, strongly unequal, outer 3 ovate, ca. 1 mm long, inner 3 elliptic, ca. 2.5 mm long, their tips incurved; the fertile stamens are glabrous, outer 6 introrse, broad, with very short filaments acute apex, inner 3 extrorse, with 2 sessile glands at base, the tip elongated beyond anther cells into a slender beak, the fourth whorl of stamens reduced to glabrous staminoda; the ovary is globose, glabrous.  Fruits are enclosed in the accrescent floral tube, dried floral parts persist in the fruiting stage. Photo (above): C. filiformis on noni (M. citrifolia) in the coastal Puna district on the island of Hawaii (Photo: S. Nelson, UH-CTAHR).

Similar plant species: Two plant parasitic phanerogams in Hawaii (two Cuscuta species of the family Convolvulaceae, the dodders) have a similar appearance to C. filiformis and a similar mode of parasitism. The most readily visible features that distinguish these two genera (Cassytha vs. Cuscuta) appear in the inflorescence and the fruits (Table 1). The flowers of Cuscuta are small, about 2 mm-diameter and are borne singly along the stem. The fruit is a dry, spherical, thin-shelled structure containing several small black seeds. Conversely, the flowers of C. filiformis are borne in small panicles. The fruit is a small, fleshy, and berry-like, bearing a single, spherical seed. Cuscuta is an annual, whereas Cassytha is a perennial. C. filiformis parasitizes mainly woody plants. With the exception of Cuscuta exaltata (not reported in Hawaii), dodders usually parasitize herbaceous plants.

   

Distribution of C. filiformis: pantropical throughout the coastal tropics; in Hawaii, reported on a variety of hosts, usually growing in coastal habitats, and documented from all the major islands except Kaho'olawe. In Hawaii, C. filiformis is indigenous. On Kure Atoll, (Northwestern Hawaiian Islands), a small patch was found in recent years on the northeastern coast as a parasite of Scaevola sericea (naupaka).  

Habitat: Coastal vegetation, usually on sandy dunes; margins of evergreen, gully and riverine forest; deciduous plateau and coastal woodlands; montane grasslands and dambo margins, and in vegetation of sandy beaches of lakes. On small bushes, woody shrubs and low trees, and on grasses and herbaceous weeds.

Dispersal of C. filiformis: Seeds may be spread by animals, water, strong winds, farm machinery or with crop seed. The plant may spread locally by vegetative growth between hosts and over soils.  Examples: (1) seeds are carried by oceans currents among and between continents and islands, or locally by streams or rivers or seasonally flowing water; (2) seeds are consumed and dispersed by some bird species; (3) seeds are dispersed by strong winds (hurricanes/typhoons); (4) seeds are consumed and dispersed in Australia by macropods (e.g., The Rufus Hare-wallaby, Lagorchestes hirsutus); (5) seeds can contaminate the seeds lots of other plant species and be planted unknowingly; (6) humans may disperse the plant intentionally or unintentionally; (7) tidal waves (tsunami) may move seeds and stems further inland from an original site of infestation. Photo above: C. filiformis enshrouding and bridging noni (M. citrifolia) plants in the coastal Puna district on the island of Hawaii. (Photo: S. Nelson, UH-CTAHR).

Survival: Seedlings of C. filiformis can survive for up to two months without a host and growing to a length of 30 cm or more.

Pathogenicity of C. filiformis to plants: The science of plant pathology treats plant parasitic seed plants as a distinct group of plant pathogens that are able to infect other plants and cause disease. Although many insects have a parasitic relationship with host plants, the relationship is traditionally defined as food relationship that does not develop further into a disease relationship. In a disease relationship between a parasite and host, the relations are more intimate; a process of infection ensues and the physiology and metabolism of the host is adversely affected. In this case (C. filiformis), disease is caused by the effect of infection of host plants by specialized attachment and penetrating feeding structures known as haustoria that are found on stems of C. filiformis and similar parasites. The haustoria of C. filiformis penetrate the host epidermis and extend into more interior tissues, extracting cellular nutrients and water from plant phloem and xylem. Even though the haustorium is an intracellular structure, it is not in direct contact with the host cell cytoplasm. In the case of phloem tissues, the cells of the plant host and the pathogen are separated by their respective cell membranes. Nutrients and fluid pass through these membranes. After the haustorium directly penetrates the cell wall, the haustorium does not penetrate or break through the plasmalemma membrane, but rather invaginates it. Teleologically, the objective of C. filiformis is to obtain nutrients from the host plant without quickly killing host cells and without interfering in more than a subtle way with their activities, or by creating immediate fatal damage to host cells and their metabolic processes (please refer to photographs of C. filiformis haustoria below). Rather, the host plants can die a long, protracted death by starvation while C. filiformis, through intimate membrane-to-membrane contact with its host and with itself, extracts what is required for it to grow, flower and produce seeds for its future generations.

Effects on host plants: Infections may be fatal. Heavy infestations can eventually smother and kill plants and the coppice re-growth in coastal habitats. C. filiformis is a threat to lowland reforestation projects. Right: C. filiformis on mango (Mangifera indica), Hilo International Airport (Photo: S. Nelson, UH-CTAHR).

C. filiformis as a vector of other plant pathogens: C. filiformis is reported to be capable of transmitting phytoplasmas from palms [Coconut (Cocos nucifera); Areca (Areca yellow leaf disease, ALD)] and a virus disease (citrus mosaic, caused by citrus mosaic badnavirus, CiMV).