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Botany Photo of the Day
In science, beauty. In beauty, science. Daily.

Aug 22, 2014: Crassula ovata

Crassula ovata

Number five in the series on South African plants and biomes series from Taisha, who writes:

The informally-recognized thicket biome of South Africa is featured today with an accompanying photograph of Crassula ovata. This image is another shared via the Botany Photo of the Day Flickr Pool, and photographed by Sean Rangel@Flickr. Thanks for sharing, Sean!

The Albany thicket occurs along the Fish, Sundays, and Gamtoos river valleys in the eastern Cape, and moves west along the intermontane valleys of inland Fold Mountains and east into Maputaland-Pondoland Bushland and thicket. Annual temperatures range from 0°C to 40°C, with it being more extreme inland, and more moderate toward the coast. Annual rainfall is between 300-550mm per year, varying between inland and coastal areas, and valley mists are common on the coast. Soils are deep, lime-rich, sandy loams that are well drained and often have low moisture levels for extended periods of time.

The Albany thicket can be divided into three regions, each with unique vegetation patterns. The dry, inland areas of the Fish, Sundays, and Gamtoos Rivers are rather sparse, and have been classified as Valley Bushveld. This region contains both leaf and stem-succulent shrubs and a few characteristic woody species. Coastal area of these river valleys, known as Kaffarian succulent thicket, are extremely dense with ~90% canopy cover. These thickets are rich with species of spinescent shrubs, woody vines and succulents. Lastly, the intermontane valleys, know as Spekboomveld or Spekboom succulent thickets, are a dense shrubland dominated by Spekboom (Portulacaria afra) with other succulents, herbs, and grasses also occurring.

Crassula ovata is one of the most common crassulas occurring in South Africa. This well-branched succulent shrub occurs naturally on rocky hillsides from Willomore to East London, and north to Queenstown and KwaZulu-Natal. From a picture of the foliage, you may recognize that this as the commonly cultivated plant known as the jade plant or money tree. Many people grow these as container plants, both in and outdoors.

Like most Crassula species, Crassula ovata reduces water loss from its leaves by utilizing Crassulacean Acid Metabolism, or CAM. Part of the CAM biological process is that stomata are closed during the day to prevent water from evaporating, and instead opened at night to collect carbon dioxide (this is the reverse of how most plant species exchange gases, with stomata open during the day instead). The carbon dioxide is stored overnight in the form of crassulacean acids, which are then broken down during the day. This releases the CO2 for the photosynthesis process during the day. During extremely dry periods, Crassula species may undergo CAM-idling, where stomata are not opened during the day or night. Instead, the plants will recycle the CO2 within the cells. This leaves them unable to grow or develop new tissue, but the plants are able to survive the lack of water by losing very little of it during this time.

Aug 21, 2014: Cunonia capensis

Taisha continues with the South African plants and biomes series. She writes:

The forest biome of South Africa is up next. To accompany this entry, we have two photographs (image 1 | image 2) of Cunonia capensis (also known as the butterspoon tree, rooiels in Afrikaans, and umLulama in Zulu) from University of California Botanical Garden at Berkeley. These were uploaded to the Botany Photo of the Day Flickr Pool by James Gaither (aka J.G. in S.F.@Flickr), who has since passed away.

The smallest biome in South Africa, the forest biome covers less than .25% of the country. Still, it is divided into two regions: Knysna forest along the southern Cape coastline, and the Amatole further east inland. The Knysna-Amatole forests are part of the afromontane archipelago--discontinuous regions analogous to sky islands. Knysna occurs on gentle slopes between 5-1220m, while the Amatole Mountains lie between 700-1250 m. Rainfall and temperatures vary between ~500-1220 mm and ~10-25°C respectively with the Amatole Mountains being both wetter and cooler than Knysna. The soils of these forests are generally acidic and nutrient-poor.

The floristically diverse forests have some 636 and 649 vascular plant species recorded respectively. Evergreen trees primarily form a continuous canopy, covering layers of vegetation that include (but aren't limited to) lianas, herbaceous species such as ferns, and epiphytes. Because of the dense shade from the layers above, the ground layer is almost absent.

A species that can be found in this biome is Cunonia capensis, the tree featured in today's photographs. Cunonia capensis, of the Cunoniaceae, is a tree found along the coast and adjacent inland areas of South Africa. In the forest it may reach up to 10m in height, and about half that height in the open. The showy, scented flowers appear in February and continue through March. They are collected in cream-coloured spikes, as shown in the first photograph. The fruits are brown two-horned capsules that release fine, sticky seeds. Seeds are either wind-dispersed or may also stick to visiting birds that fly off with them attached to their feathers, legs, or bills. One of the more prominent characteristics of Cunonia capensis is the pair of stipules that enclose the growing tip of developing branches. They are large and are pressed together and look much like a spoon--hence one of the common names, butterspoon tree. The second photo shows this phenomenon, as well as additional images via the Fernkloof Nature Reserve site: Cunonia capensis.

Aug 20, 2014: Mimetes cucullatus

Here is Taisha again, with the third entry on South African plants and biomes. She writes:

Today we feature two photographs of Mimetes cucullatus, known as the common mimetes or pagoda or the red mimetes or pagoda. In Afrikaans, this species is known as rooistompie, or simply stompie. Rooi means "red", and stompie means "little stump". Retired UBC Botanical Garden staff member, David Tarrant, sent these images from his visit to Cape Town's Kirstenbosch National Botanical Garden last November. Thank you kindly, David!

The fynbos is a biome located in southwestern South Africa. It consists of two distinct vegetation groupings, the fynbos and the renosterveld. These regions together form over 45000 km2 of land, all above 300 meters in elevation. Renosterveld typically has fertile, fine-grained soils of silts and clays whereas fynbos has poorer nutrient quality. Rainfall occurs throughout the year and accumulates anywhere from 300-2000 mm annually. Fire is an important influence on fynbos community processes, and the region must burn every 6 to 45 years to sustain many plant species.

Mimetes cucullatus is an example of a plant that relies on fire for regeneration. This is the only species of Mimetes that is a resprouter (as opposed to only being a reseeder). After fire, plants regenerate from a large, woody, underground rootstock, whereas most others are killed by fire (unless they have a thick, corky bark and survive). Seedlings will also sprout post-fire when conditions are suitable.

Common mimetes is a widespread species. It is easy to distinguish from other members of the Proteaceae with its unusual tubular and wool-like flowers grouped in four perianth segments. In bud, the segments touch each other, but do not overlap. They then separate as the flower opens to expose the style equipped with a sticky pollen presenter. Stigmas on these perfect flowers are not receptive at anthesis, thus preventing self-pollination. Within each of the white tuft-like perianth segments rests a single anther. Colourful leaves surround each floret like a hood. After pollination by sunbirds or sugarbirds, a nut-like fruit develops. The seeds within the fruit have elaiosomes (grey-white oily protuberances) at either end. These eliaosomes attract ants, who collect the seeds to carry back to their underground nests. There, they eat the elaiosomes, but do no damage to the seeds. Seeds deposited in ant nests can remain viable for many years.

Aug 19, 2014: Pachypodium namaquanum

Pachypodium namaquanum

Second in the series on South African biomes and plants, again written by Taisha:

Pachypodium namaquanum is commonly known as halfmens (Afrikaans for "semi-human"), elephant's trunk, or elephant plant. This species is found in the Succulent Karoo. Drew Avery@Flickr took this photo back in 2009 at the Denver Botanic Gardens and shared it via the Botany Photo of the Day Flickr Pool. Thanks, Drew!

The Succulent Karoo biome extends down the western coast of Namibia and further inland and comprises two domains--the Namaqualand-Namib domain along coastal plain, and the Southern Karoo domain to its east. The altitude of this region is mostly below 800 meters, but may reach up to 1500 m. The temperature in the Succulent Karoo ranges from -4°C in the coldest month and can reach over 40°C at other times. Annual rainfall ranges from 20-400 mm and falls mainly in the winter months (summers are arid), with heavy fog supplementing the precipitation. Berg winds may also occur throughout the year. Soils of the succulent Karoo are much like the Nama Karoo--lime-rich, weakly developed soils on rock.

The vegetation in the Succulent Karoo is, as you may have deduced, dominated by succulents (particularly dwarf shrubby species)! There are many leaf succulents present in the Succulent Karoo, and annual displays of asters occur in the spring. Endemism is extremely high, with around 67 genera and over 1,900 species occurring nowhere else. Included amongst these endemics is Pachypodium namquanum, the species in today's photograph.

Pachypodium namquanum is a stem-succulent species of the Apocynaceae that can live up to 300 years or more. This species grows slowly and regularly, eventually attaining a tree-like appearance when mature at 1.5 to 2.5 m in height (see photos linked from the Wikipedia page: Pachypodium namaquanam). The stems are also covered in tubercles, from which spines protrude. The leaves are borne in rosettes and are distinctively wavy. Yellow-green flowers with red interiors appear from July through September and later develop into horn-like, dehiscent capsules enclosing wind-dispersed seeds.

The unusual appearance of the halfmens has made it one of the most famous and sough-after succulents in the world. One of the most intriguing characteristics is the bowing of the stem to the north. There are folklore interpretations of this phenomenon, however researchers attribute this nodding of ~45-65° to the low solar zenith angle during the winter months. They explain that during the winter, where conditions are more favourable for growth over summer, the low solar zenith angle may pose a potential limiting factor on plant growth. The 55° north incline, they explain, would maximize the solar irradiance on the plane of whorled leaves, of which most are also on an inclination to maximize irradiance. The researchers suggest that the slant northward may benefit the species by increasing net primary production, as well as increase tissue temperatures midwinter when the flowers and later fruits are developing thus minimizing the effects of late-season drought on reproductive output (see: Rundel, P., et al. (1995). Winter growth phenology and leaf orientation in Pachypodium namquanum (Apocynaceae) in the Succulent Karoo of the Richtersveld, South Africa. Oecolgia. 10(4):472-477).

Aug 18, 2014: Aloe broomii

Aloe broomii

Taisha begins a series on plants and biomes of South Africa today. She writes:

This photograph of Aloe broomii was uploaded to the Botany Photo of the Day Flickr Pool by MarieVijoen@Flickr--a frequent contributor sharing photos of flora from South Africa and New York. Thank-you, Marie! (and here is her weblog for further reading: 66 Square Feet (Plus)

South Africa has eight major terrestrial biomes (PDF): the Nama Karoo, succulent Karoo, fynbos, forest, thicket, savanna, grassland, and desert (see map). These biomes (large-scale biotic communities) each have distinct climatic and environmental conditions. Correspondingly, each biome has a flora and fauna with different adaptations.

The first biome in the series is the Nama Karoo. The Nama Karoo is an area on the central plateau of the western half of South Africa. The Nama Karoo is the second largest biome in the region and is divided into three main subregions: the Upper Karoo, the Great Karoo, and the Lower Karoo. The altitude is between 500 and 2000 m with most of the area between 1000-1400 m. Most of the rain falls in the summer months between December and March, and temperatures may reach over 30°C. In the mid-winter (July), temperatures may be below freezing. Shallow and weakly developed lime-rich soils cover most of the region.

The vegetation type of this area includes many dwarf shrubs and grasses. This area is not particularly species rich, although much of the flora is adapted to the local climatic extremes. One of these plant species is Aloe broomii, of the Xanthorrhoeaceae. This species is also known as the snake aloe in reference to its snake-like racemes. Aloe broomii has unique flowers—the buds are hidden from view by longer bracts, and only the stigma and styles peak out awaiting pollination by visiting bees, sunbirds, and ants. These pollinators are attracted by the nectar. The many light-winged seeds of Aloe broomii are dispersed by wind and may be consumed by small maize or rice weevils (Sitophilus spp.). Some farmers in the Steynsburg district will boil the leaves to extract a brownish fluid. This fluid may be used in a number of ways: to kill ticks, as a disinfectant, as an ear remedy for sheep, or given to horses in small doses to make their blood temporarily bitter, causing any ticks to disengage from the animal.

Aug 13, 2014: Saxifraga flagellaris subsp. setigera

These photographs were taken during my mid-July field work in northern British Columbia. Sometimes evocatively called spider saxifrage, another common name for Saxifraga flagellaris is stoloniferous saxifrage. The spidery stolons are a means for vegetative propagation, with genetically identical individuals to the parent sometimes becoming established at the growing tips. This can be considered an adaptive advantage for growing in alpine environments, where a preceding winter with heavy snowfall or an abbreviated wet, cold summer can limit the amount of time a plant has to grow and reproduce. The presence of additional clones can be predicted to increase the chance of reproductive success (through higher quantity of flowers) and the year-to-year survival of parent plants. Being myophilic (fly-pollinated) like many other high-latitude/high-altitude flowering plant species also helps, as flies are abundant and active in Arctic and alpine environments.

The Flora of North America notes 8 subspecies of Saxifraga flagellaris are recognized, and suggests that subspecies setigera is native to northwestern North America, Siberia & the Russian Far East, and Svalbard. Other references, such as the Intermountain Flora, throw out the idea of using subspecies for this taxon, citing few geographic correlations. To me, today's plants do look different compared to the US Rocky Mountain subspecies, Saxifraga flagellaris subsp. crandallii, but it isn't enough to compare a few individuals to determine whether similar-appearing plants should be lumped into one taxon or split into many. One might be looking at the extremes on either end of a range or cline, so it is necessary for taxonomists to do exhaustive comparisons of the characters of herbarium specimens in order to form a scientific assertion that will stand the test of time. Clearly, disagreement still remains.

Aug 12, 2014: Castilleja lemmonii

Castilleja lemmonii

I've returned from two weeks of work in the field and two weeks of vacation, but here is another entry from Taisha today while I continue to catch up on correspondence. Taisha writes:

Thanks to Eric Hunt.@Flickr for this photograph of Castilleja lemmonii, or Lemmon's Indian paintbrush. It was taken in July of 2009 in an alpine meadow between California's Greenstone Lake and Saddlebag Lake, located in the Inyo National Forest of Mono County. Thanks, Eric!

Castilleja lemmonii is perennial species native to California. It is found in moist meadows in the southern Cascades and the Sierra Nevada at elevations of 1550-3700 m. Grey-green lanceolate leaves are held on an unbranched stem that can reach up to 20 cm in height. The inflorescence consists of a collection of pink to purple-red bracts that surround green tubular flowers.

Members of Castilleja are placed in the Orobanchaceae, but many older texts had them classified in the Scrophulariaceae. They are hemiparasitic, i.e., photosynthetic, but also receiving some nutrition from host plants. Castilleja species are noted to parasitize a wide range of plant species, and can also parasitize multiple hosts simultaneously. More specifically, Castilleja species are facultative root hemiparasites. Their roots grow until they touch the roots from another plant, whereupon they penetrate the roots with haustoria. The Castilleja receive water, fixed carbon compounds, nitrogen, other nutrients, and even secondary metabolites from the host.

Hemiparasites influence plant community dynamics and other trophic levels by a distinct suite of ecological traits. Most people may initially suspect that parasitic plants have mainly negative affects within a community, particularly with respect to their hosts. This is true to some degree where the parasitic plant competes with both host and non-host plants for light, water, nutrients, pollinators, and seed dispersers. However, according to some ecologists, parasites may actually increase the diversity within a community depending on whether or not the preferred host is the competitive, dominant species. If dominant, then its suppression of the dominant species may allow for other species' populations to increase. Hemiparasites are also sometimes considered mutualists. The litter of hemisparasites is considered to be nutrient rich, and as this high-quality litter rapidly decomposes it provides nutrients for co-occurring plants. It also supports a more diverse and active soil biota.

To read more, you may wish to look over a paper by Phoenix and Press from the University of Sheffield where they discuss several aspects of the influence of Orobanchaceae on community dynamics (see: Phoenix, G., Press, M. (2005). Linking physiological traits to impacts on community structure and function: the role of root hemiparasites Orobanchaceae (ex-Scrophulariaceae). Journal of Ecology. 93(1): 67-78). You can also read a summary of their paper written by a graduate student from the University of Washington last year.

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