T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Digitaria sanguinalis (Summer grass)

Kingdom: Plantae
(unranked): Angiosperms
(unranked): Monocots
(unranked): Commelinids
Order: Poales
Family: Poaceae
Subfamily: Panicoideae
Tribe: Paniceae
Genus: Digitaria
Species: D. sanguinalis
Binomial name: Digitaria sanguinalis
Common names: Summer grass, Large crabgrass, Crab finger grass, Purple crabgrass. Crabgrass.

Digitaria sanguinalis is a species of summer-annual, sub-tropical grass native to the warmer regions of Europe and Asia. It is known nearly worldwide as a common weed. It was introduced to New Zealand over 100 years ago. In the North Island of New Zealand, it is very common in the northern and coastal regions where it forms dense patches on roadsides or in waste ground. It is one of the most prevalent summer-active grasses in Waikato, Bay of Plenty and coastal Taranaki dairy pastures. It is also common in parts of Canterbury and Otago but scarce elsewhere in the South Island.

Digitaria sanguinalis germinates in late spring or early summer and grows as a prostrate rosette. The flower stems often sprawl along the ground before growing vertically. It rapidly produces very long, very thin, radiating inflorescences (3-13) that branch from more or less the same point atop of the stems. Each branched spike is lined with pairs of very tiny spikelets. The inflorescences may be reddish or purplish. The flowers are a pale grey or slightly purple in colour and they have mauve coloured filaments and anthers.
The stems are smooth and hairless between the nodes. The stems when they are close to the ground will often produce roots at the nodes.
The leaves blades are broad and comparatively short, soft and are green to greenish-purple in colour. They are widest about 10 - 20 mm above the ligule, then tapering to a point. The young emerging leaves are rolled. The leaves and stems often have patches of red-purple pigment.

Summer-active grass species, such as Digitaria sanguinalis, have a C4 photosynthetic pathway. This allows them to grow more quickly than other grasses in response to increasing temperatures and solar radiation if given adequate rainfall. Their water-use efficiency is also higher than that of other grasses, making them more tolerant of drought conditions.

New inflorescences before branchi

The radiating inflorescences 

The flower is bisexual. It consists of an ovary containing 1 ovule (the female part). The ovary is surmounted by two purple feathery stigmas and is surrounded by three stamens. Each stamen (the male part of the flower) consists of an anther (image here) and a filament. 
There are no petals or sepals. Instead, the flower is protected by two sets of scales. The first set consists of the LEMMA and the PALEA which enclose the flower. This whole structure is called a floret

The leaf node.  The lower portion of the leaf forms a sheath, which encloses and protects the young shoots. The second half of the leaf then opens out into the leaf blade.

A diagram of Digitaria sanguinalis (Summer grass)

Thanks to AGPest & Wikipedia for text and Information: